Legal Question in Family Law in California

What you can do is file a motion to modify custody. Whether you will be successful or not will depend on the exact nature of the boyfriend's crime, when it occurred, and ultimately whether that would make it inappropriate or unsafe for your daughter to be with your ex with him around. Penal Code section 288(a) is a very broad-brush statute, and also may be a plea bargain conviction from something like statutory rape. So there is no way to tell from your question whether this guy is a hard core kiddy-freak, or a poor sap who had to plead down from statutory rape twenty years ago when he was 18 and his 17 yo high-school girlfriend got pregnant.