If not offending the family is all, I'd send DH on his own.
There's no way I'd want to be in the company of someone like that myself, before you even begin to weigh up the risk factor towards any children attending. What happens at most weddings ? ..... people circulate, you get talking to all sorts, what do you do if BIL's wife takes it upon herself to introduce this man to you ? Turn heel, and then cause a scene, or a future rift ? ..... 'cos no way would I even begin to countennance small talk with a convicted absuer.
If I attended in those circumstances, I don't think I would be able to take my eyes off him at all (though that'd be the last thing I'd want to do obviously). It would be horrendous ..... how would you feel if you loose sight of him, and then start wondering where he's gone, or what he might be up to ? At some point he would need to go to the loo - and I'd be thinking, who else is in there, were there any kids in there ? At your typical wedding, kids are running about excitedly all over the place, not sitting quietly with mum & dad. You can bet I'd be watching my own like a hawk, but I would also be feeling responsible for every other child there.
The actual probability of anything untoward happening is not the point - I would feel sick just to observe him watching children and I think the whole day woudl be excrutiating.
I wouldn't go unless I was told he wasn't going to be there, and if he turned up, I'd leave .... though I'd also feel a huge moral responsibility towards all other guests there with children. Which begs the question, if he does go, but you don't, I would still feel terribly concerned about other parents & children going who may not know his history - you'd have to try and tell them wouldn't you, so they can make an informed choice ...... or else, despite the (probably) small risk of something happening, you'd never forgive yourself if something did happen and you'd known.