suddenly resisting sleep at night

Could anything have changed in his normal routine, like starting a new nursery, or a new baby coming , that type of thing?? Maybe he is having bad dreams ? I know it sounds cliched and I am sure you have already tried it, but a steady normal unwinding, book bath bed, the usual drill. Maybe one to one time during the day, and getting him into his bedroom on a casual basis, like putting away his clothes , looking for a book etc etc. Sorry can't be more helpful . It is unusual , but I am sure things will settle . That age group do be a bit erratic with their sleep routine and it doesn't take much to knock them off.

If he still has a daytime nap maybe cut it out so he’s more tired after teatime?

Oh dear, never expect that good sleeping habits with toddlers is going to last. It rarely does unless you're lucky. Let him play for a bit longer in the evening then quieten things down with a story.
These lighter nights are the bane of a parent's life as in a child's head it's daytime/playtime.

Good point EV

We had a terrible time with our third child, she would never go to bed, she never seemed to be tired, we went for years, with one of us getting up for a couple of hours during the night with her, so she wouldn’t keep the whole house awake, and then would be up again at 5.00, the sleep she did get was generally in our bed

If someone had told me their child was like this, I’d have been absolutely scathing, and said it was ridiculous, but we tried everything possible, all failed!

She didn’t sleep all night till she was seven!

I’m not telling you this to scare you, I’m sure your problem is temporary, but sometimes you just have to go with it, it seems you can’t force a child to sleep!

Keep him up a bit later, then put him to bed with toys & books and leave the light on. Say he doesn't have to sleep, but has to stay in the room. If he comes out, take him back gently but firmly.
May not work, all kids are different, but you mustn't show you are worried .

I had this problem with both my grandchildren, and I can vividly remember it with my second child. With my grandchildren, I said “night night, I’m going t o load the dishwasher, then I’all come back.” I made a lot of noise loading the dishwasher, and they stopped crying and dropped off. With my daughter, I sat on the landing with a book and went in and settled her every ten minutes. It took a week of this, but it worked.

This too will pass jeanerskine toddlers are always erratic with their behaviour, eating, sleeping, toileting so try not to worry. Check there is nothing he is afraid of in his room, keep calm and stick to a soothing routine as clementine said.
Fast forward a few years when he is a teenager and you will be lucky to get him out of bed before noon.

I can't find that anything has changed to his usual habits. He's slept soundly and happy to bed for the last 2 years - it's a very sudden and dramatic change...

The fact that he’s slept soundly for two years makes you all very lucky mine were all erratic sleepers and it’s very rare to go through all childhood with a good sleeper it could have been as simple as a bad dream from a bit of over stimulation causing one bad night and changing his good habits It could be a tv programme even a story that’s spooked him if he goes to nursery something there could have triggered an anxiety
Often brilliant sleepers as babies make up for it in toddlerhood or vice versa
Me personally would comfort him and if necessary stay with him till he drops off if he’s really distressed I know others will say don’t do that but I d prefer to sacrifice an hour of my time to get the child to a comfortably drop off point again when mine woke distressed in the night they would co sleep with me or I with them others won’t agree with that
Everyone will have different method but the main thing is it will pass and as soda pop says forward wind a bit and you won’t get them out of bed Don’t get hung up on it your concern will rub off on him

I agree Bluebelle, do what you have to do, if we hadn’t let our daughter sleep with us, none of us would have any sleep

I wish there was a like button Sara I couldn’t manage with so little sleep, three children, and no support and I have three healthy ‘middle aged’ children who have managed what ever way they chose I know at least one played musical beds too 😂

Blue belle, my troublesome little sleeper
has three children of her own, and they all sleep like little angels!
There’s no justice!