How do I hadle contact between my husband and ex-girlfrined, the mother of his kids?

I still don't know how to handle mine :(

You have to be the 'bigger' person by being understanding and supportive and realize that he IS the kids daddy. If you don't get along to well with her or do not trust her, when you have to deal with her be short, sweet and to the point rather than going on and on.
IF you suspect that they still have something going on don't be accusing just watch for signs until you are positive.

How do i hadle contact between my husband and ex-girlfrined, the mother of his kids?

As hard as it may be for you, SHE will always be the mother of HIS children. If they are young children, they will remain in contact (and should) for a very long time. I have learned to be cordial to my boyfriend's ex-wife, it makes for an easier transfer/drop off the children and the children observe the interactions. You must learn to live with this and not be jealous, after all, YOU are the one he is with, right? ;)

I think that you should sit her down and have a long talk with her. Most women are already uptight to the other women because they feel that they want to take their place, or they don't want them to even be around the children. I think that you should let her know that you are not there to take her place and that you respect her as the mother of his kids. If you love that man then of course you love what's his and that's the kids. I know that you are going to probably read this and go... whatever but it works. Be the bigger women and don't let something so small grow into something so silly.