new boyfriend

So I started seeing this guy and he's got a 3 year old son, I'm 20, he's 22. The child is down every weekend and I love spending time with them. But the child's mother does not have him in a routine, no bedtime and he doesn't eat, and when he's at his mums she just gives him bottles of milk! He's nearly 4!! Me and his dad have tried getting him into a routine when he's with us but it's all messed up when he goes home to his mums for the week. It's so frustrating!! Sorry needed to vent lol