My fiance doesn't make an effort to see his children of a past relationship

I met my boyfriend very early after he broke up with ex girlfriend of whom they share 2 young children. Unfortunately he was not very honest with her about his new relationship with me and she found out with what turned into a very messy and physical incident. A year and a half has now gone by and he still hasn't seen his children. She has not made it easy for him sending back Christmas and birthday gifts sent to her relatives houses and changing her address and phone number. I know if he tried he would be able to find them but he gets quiet and irritated whenever I try to address him about it. His ex doesn't have the best history and it's a worry of mine that if he does turn up at her address that she will be violent. I love him and would one day like to have children of our own but it eats me up to see that he isn't going out of his way to fight for his children. Any advice would be appreciated

i guess he needs to decide about this,leave it to him its between him and her now