I'm not sure if I'm posting in the right area, but I'm a single parent so thought I'd stick it here.
I split from my kids dad when they were 2 and 10mths old. He was having them every other weekend, he lived locally and this was fine, though occassionally ds would be brought back with his sisters purple patterned trousers on and so on 
Ex moved away (300 miles away) after a few months, saying he would still see them, he didn't bother though, and when he did it was once every 4-5mths, I refused this and he threatened to take me to a solicitor. I beat him to it though and got some advice, I was basically told that I did not have to let him have access due to the relationship together (domestic violence) but I said I wanted him to have a relationship with the kids, just regular!
It was agreed (after a couple of months) he would have supervised access, he was entitled to 2hrs a fortnight at a contact centre.... this went on for just over a year and I told him he could start taking them out for the day, nothing more, just spend more time with them both rather than cooped up in a hall with little to do.
He gradually began to mention the idea that he could take them to his during the school holidays, I was very unsure but eventually agreed. He had them for 1-2wks at a time, we split the holidays and he had them one christmas, I was trying to be fair.
He obviously got bored of this arrangement and has gone back to seeing them every 3-4mths now, though he is asking if he can have them for 3wks in the summer hols....they haven't been to his since last summer hols (nearly a year ago) and I don't want them to go. Yes, I am shattered (ds is autistic) but I don't trust him. DD (6) was telling me the other day 'Daddy doesn't shout at us when we argue, he is normally sleeping, but he wakes up when Big Barn Farm comes on the tv'
DD obviously didn't know how wrong that was, and I am disgusted that he done that, he has fallen asleep with them 2-3 times before and I have made my feelings perfectly clear about it.
Anyway (sorry for the long winded post) .... after all that, does anyone have any advice on what to do? Do I just cut contact? Recently he's been seeing them every 3-4mths, he comes down for the day and goes again, the kids are not bothered about his arrival nor him leaving.....
I don't really know what to do, anytime I speak to him he says he'll sort it etc and never does...