Sorry if I'm misunderstanding, but do you mean on walks? If yes I would put him definately in a sit or drop position. I use sit as the first port of call.
I find it an easy point to gain attention, and get their focus on you. I wouldn't purposely go up to or pass close by a group of kids until you have got your dog to focus on you and be sitting quietly.
What is the dogs distance factor? (critical distance). What I mean is how far away does a group of kids have to be before he/she starts the barking? You can use the distance factor to your advantage in his training. If for example a group of kids are at at distance, and your dog has noticed them. Get him to sit and try to find a cue word for him to look at you. Make you the total focus of his attention. I use "looking" for Max, after I've put him in a sit position
As time goes on and with perseverance his critical distance will decrease, and he eventually won't want to yank your arm off, or bark his head off at the kids LOL. Always praise as soon as he has sat/dropped and has turned his head to look at you. I used some treats with Max till he mastered the looking command, and of course don't use the treats now.
My Maxy hates bikes, push and motor. He is fine with them in the distance, but not when they are upon him. Unfortunately some people on pushbikes will be coming around the corner and almost knock you over. It didn't help that the postman on his motor bike almost ran us both down one day. When I see one coming, or know one is coming around the corner headed right for us, I move Max slightly and put him in a sit position, use the "looking" command, and praise immediately until the bike has passed. He has improved greatly with this.
Please bear in mind I am no expert, but this is just my personal experience over the years, and what has worked for me
Others I'm sure that are more experienced in training will have some other methods/tips for you as well, I'm sure
Good luck with it.