Can exp keep dc without my agreement?

[Baabaapinksheep]

Dc are due to go and stay with exp for a night in the Xmas hols, he wants them for two nights but I only want them to go for one night. My reasons for this are: he has only seen them about once a month for an afternoon at a time in the last year (he lives quite far away); they went to stay with him for a night a couple of months ago, this was the first time for years; they will be knackered when they get back as dd1 doesn't sleep well in places she doesn't know, and if they go for 2 nights they will be coming back on the Xmas eve.

We gave agreed that they will just one for one night, but exp said he could just keep them for two nights anyway. Can he do this? What are my rights?

Dc are 4 and 5.

i don't get why ex's think they can do nothing all year and then have loads of contact at christmas. why should we do all the hard work and they get all the reward. children are for life, not just for christmas! i think building it up from one night is right, not throwing them in at the deep end at the most happiest/stressful time of the year.