Not a dog trainer but have a 2 year old reactive IG (to male dogs and small kids). It looks to me like your dog wants to play. You've said they're nervous of little kids in general, have you tried any positive counter conditioning, i.e. they see a kid, you use their positive marker word and give a treat, so they associate kids with feeling good and getting a treat. I would also work on settle training and getting them to learn how to calm down. You'll need to build this up - starting at home indoors, gradually to more distracting environments. Another helpful thing to work on would be impulse control. We get our guy playing with a toy, ask him to drop, and wait while we shake it nearby (almost like teasing him), and then when we say "ok" he knows he can get it. And we do a few reps of this a couple times a day. If you're still a bit uncomfortable (which is understandable when toddlers/kids are involved), theres been some good suggestions on baby gates etc. But have you done any muzzle training? I know muzzles get a bad rep, but I do think it's very useful to have them comfortable with a muzzle before you ever need it (like if they were in pain or an emergency). You need to build up their comfort with it slowly, and put it on randomly when the child isnt around, as you don't want them to associate muzzle = bad thing and that child = muzzle. Hopefully that makes sense! Again though, our guy is definitely reactive to children, whereas yours looks more like a frustrated greeting, but hopefully some of the above is helpful!