Don’t know how to feel

I assume that none of you live in the UK? Camping in December or January would be more of a punishment than a treat ! Although, my brother and SiL have often been in their caravan on Christmas day!
I'd guess he was thinking that no firm arrangements had been made for you to go and stay, or just that they will only be away from home Christmas day and Boxing day - travelling to you would mean that he would have to take more days off work if he has no leave left.
Just hope that they have a great time and look forward to a second christmas with the GC in January!

He could of already booked that off as holiday weeks/months ago. It could of been planned for a while and forgot, felt guilty and didn't say anything.

It could of been a few days holiday.

He could just want a holiday instead of hosting.

There could be lots of reasons. I honestly wouldn't worry.

How long is the camping trip? Maybe DiL had arranged it with sister and DS didn't know, at the time he spoke to his dad.

Or Son said "It would be nice" and then forgot about it as it hasn't been made definite.

If your son has a good relationship with you both, I expect there's nothing to worry about.

Gone girl, the reason I didn’t call my son out on the situation was that there is a possibility that the decision to go away camping was my daughter in laws as it is her family that appear to be accompanying them and I did not want to put my son on the spot or make him uncomfortable
And Flexible friend, I understand what you are saying but ...he forgot ? We only are able to visit once a year and he forgot? Hence my struggle

Could you perhaps afford to go away somewhere really nice yourselves? Not horrible camping of course. A really nice hotel somewhere.

No need to keep it a secret from son either.

Why didn't you say, "Oh, I thought you'd used up all your holiday leave"? I would have done. Better out than in.

Why do people pussyfoot around each other so much?

Too late now. No Christmas presents for them then.

Why try and second guess? Just assume he forgot about you visiting and has accepted an invitation to do something with his kids. There's no point fretting about it. Just visit in January and enjoy yourselves, way too much is made of Christmas.