My ex wife is wearing skimpy bikinis around me when we're hanging out with our kids, is she into me again?

You have control.: First, hang out where bikinis and seductive clothing ( or lack of enough clothing) are not acceptable. That can be done discreetly so that it would be hard to object to and wouldn't risk picking a fight. Next, stop thinking of yourself, think of the children. They more than likely sense what, if anything, is going on so support them by preventing it. It will be best for everyone.