Just keep bringing him around kids. For a while try for mainly kids who are accustomed to big dogs. Your pup is still very young, it's going to be another few months before he's learned bite inhibition 100%, and a few months after that before he's through his worst puppy stage. He'll get it though.
Caney used to jump on kids when she was a puppy. She really never got the chance to be around kids. When she was about a year old, I was walking her through the park and we passed a family with some young kids (she hadn't seen children in quite a while) and I wondered what she would do -- she just walked right up and sniffed their faces. Didn't lick, didn't even jump. She's just as tall as them now so I guess she doesn't have to

But even with older kids she doesn't jump -- we just came in from the front yard and the neighbors' kids (elementary and middle school age) ran over to pet her, and she didn't jump at all. She is very behaved around little people!

I am honestly amazed that she seemed to just grow out of it, without a whole lot of training or exposure to children. But I'm very proud