***need someone's help*** My kids school is by their "fathers" house. So today when I go for them at…

***need someone's help*** My kids school is by their "fathers" house. So today when I go for them at my moms house my mom tells me that my oldest seen his dad at the park they have in the school for the kids.. I freaked because he's not in their lives he's always been a drunk & never has wanted to help financially even when I didn't work it was hard for him to give up money & if he did the most he'll give was less then 100$ for both sometimes even just 20$ that with two kids 20$ ain't shit!! But even like that I would still let him take the boys some weekends whenever he felt like taking them just because I didn't want to seem like a bad mom & let them be with their dad & have him in their lives, but I got so fed up that I stopped letting them go with him & he hasn't even bothered asking for them to take them on the weekends either which I don't care cus i can have my kids with me 24/7 my thing is he's in their birth certificate & without court order he can go for my kids at school even not being in the list & I'm scared that the teachers aren't going to be paying attention one day when the take one of them outside & he's gonna be around again and end up taking one of them & leaving from town with one of them which I know he's capable of. I know the best is to go to court and fight for custody & try and have him away from the kids but I don't know what are my chances of winning a case like that..