hi! i'm new here et love this site! i had to write to you to say first off your dog looks fine. ive had 4 boxers, not counting 2 litters with a total of 14 pups in all. im no expert, but boxers have such a high metabloism they are almost always that thin. my first boxer didnt really start to put on weight until he was 5 et calmed down. even then he just put on muscle. my GSD on the other hand is a different story lol. as far as getting your boxer to stop nipping the kids..i had to teach both my kids et the dogs together. my kids now know the "rule of thumb" with boxers...you run from boxers, they WILL chase you. not to intentionally be aggressive, but in my experience they are VERY play oriented. we use toys a lot, ranging from tug ropes to balls (be careful with more then one tennis ball at a time though because a boxer can et will fit up to 3-4 in their mouths et could possibly choke). as the dog grows et the mouth gets bigger soccer balls are good, but invest in stock because they can easily bust them lol. we change toys a lot too, because our boxer has the attention span of a nat, so we try to keep her interested with variety. like i said, i'm not an expert but i hope my experiences could help you.