How would you deal with this…..

For a start, I wouldn't attend the ceremony if I was his mother. What a terrible deceit and a dreadful start to married life. He's building this on rocky foundations and it will crumble. It's quite possible that the new wife wants a baby, hence the rush. His children will never forgive him and rightly so. Say you will not attend a ceremony based on a lie and tell him he's being a fool. Perhaps their mother should have full custody?

A big fat NO NO NO from me.

My husband and I actually did this and the two children we had already (his daughter, my son) were very very upset and to this day berate us about it!

If we could go back we’d do it all very differently.

He is madly in love, he is rushing off to marry the new love of his life pdq, he can see no reason why he should tell his children.

Does he know the saying 'marry in haste and repent at leisure'. the repenting may well include finding he is completely extranged from his children from his first marriaage.

I think this young(?) man should really grow up himself, start thinking of his children and put them first before it is too laate.

I am wondering if your son’s first wife knows of his plans? If she finds out, and I’m assuming they live in fairly close proximity, if they share parenting 50/50, she’s likely to tell the children and put her own spin on how she sees it.

Your son really is being a fool, that kind of secret is unlikely to stay secret for long.

My eldest son did a similar thing, married his second wife (who I liked much more than the first) without telling his children. I didn't agree with that, especially as her two were involved in everything. I thought maybe it was because money was tight and offered to pay for taxi to get them to the reception/home etc but I was told it was none of my business. This was 2009 and he broke contact, I have been in touch once in all those years because he was left some money. He told me then that he had very little contact with his children from first marriage, as I suspected would happen. We did not attend the wedding.
Another friend was the mum of boys that this happened to, their father remarried without them knowing. They were so hurt, angry for quite a long time, and although they see him once in a while (he lives in U.S) it was never the same between them.

Your son sounds extremely juvenile. He is not telling his children he is getting married because he knows it will upset them, but he is still rushing into another marriage before the dust has settled on the last one. His children should come first at this time; absolutely no question.
Their life with him is one upheaval after another.And is his girlfriend/fiancee/ soon to be wife happy with this arrangement?
How soon do they plan to tell these unhappy children what has happened?

Refuse to go to the wedding unless he tells his children; you cannot be complicit with this deceit.
Be prepared to pick up the pieces of your grandchildren when they find out.
No wonder there are so many broken homes today when a parent behaves like this.

I agree with everyone that he should tell them. or if he really can't face that & you are very close to the family, to let you tell them & explain he is so worried about their reaction that he's got a mental block about telling them but he does want them to know.For him to get married without telling them when he's their 50/50 carer parent, can't really be defended.
However I would go to the wedding whatever. He is your son - to refuse to go, if it comes down to that, I would feel disloyal to him..

I have a son who is divorced with children a similar age to your gc. I imagine that I would feel just as you are. My relationship with the children would take priority in this situation. I would not be able to attend without the gc knowing of the marriage ahead. I value my close relationship with my gc, one that has been built on respect and trust. I would never do anything to jeopardize it. I'd explain this to my son. From there it's in his court. Hopefully he will respect his children by letting them know. My concern is that he has left it too late. The children will need time to come to terms with it. Waiting to tell them is unfair to them and their future step mother. This will make it harder for all of them and consequently, the marriage, in my opinion.

No No no he must tell his children or he will loose their trust forever, also if you want to maintain any communication with them you all need to be upfront, why does he feel that he needs marry so soon into the relationship? Everyone in the first flush of love is "madly in love" it is what happens later in the relationship that matters.

I think this is something for your son to sort out. Do I think he is in the wrong here? Absolutely. However, his children are not babies. If they get upset because you knew and they didn't, I'd suggest you say to them that their father is an adult, that what happened is between him and them, and that it's not your place to question how he parents.

Your son really needs to speak with his children before his wedding. It’s not fair to ask you to keep this secret. It coukd affect your relationship with the gc if you go to the wedding without saying anything to them as well as with your ex dil. Have you considered declining the invitation?
Lots to think about.
It seems very soon to marry after his recent divorce, is there a reason, pregnancy perhaps?

Wow MeowWow , I fully understand your feelings about this. Not telling his children he is getting married is his choice but IMO not a wise one! I find this situation bizarre and unreasonable. I sincerely hope that the damage caused by this will not be permanent. Your son has placed a heavy burden on you by asking you not to tell your GC. That is very unfair! You are in an impossible position, if you tell your GC you are going against your sons request but when your GC discover you knew all along they will not be happy. I agree with BlueBelle - sound advice. I wish your well in this dilemma , I fail to understand your sons decision.

I would gently point out to my son that he might later, regret not having included the children, as it will come out that he has married is girlfriend. What I mean is - he may regret the message that is being sent by excluding them from this happy occasion.

Oh wow that’s not fair at all, not fair to the children and definitely not fair to you.
I can’t imagine how you can follow his rules and not hurt the children I think I d have to say I ll come to your wedding when you ve told the children otherwise I going to be really really sad to say I won’t be able to come myself but I hope you have a lovely day.
It’s really really wrong for him to load this on your shoulders

I think he is wrong not to tell the children. After all, they will find out sooner or later. You think they will be devastated but they will be more upset if your son isn't honest with them. Do the children live with their Mum in the main? If so, this will make things a bit easier. It is not up to you to tell the children as this may cause friction between you and your son but you must urge him to do so. Children do like honesty and at 13 and 15 they are old enough to understand some of what is happening. I hope your son is happy forever in the new relationship and I imagine they have booked the wedding but it does seem rather sudden. I wonder who instigated the divorce. If it was the ex-wife I hope your son is not trying to show her that he is capable of getting someone else and trying to prove a point. I do understand your predicament. Whatever happens you will be there for the children and that is the main thing. Children are extremely adaptable.

I find it very sad that your son won’t be telling his children that he’s getting married, can’t really get my head round it, it’s a huge step! How are they going to feel when they find out, very hurt and upset I would have thought. So what is their in effect step mum going to be known as. His girlfriend? And when does he think is the right time to tell them, because they will find out probably quicker than he realises, news does travel fast.