messenger bags are good for everyone. For kids I will use a basic fabric for the outside (denim is always good). I line it with something that works for that particular kid. If he likes the outdoors, I would use fishing fabric or camo fabric. If they are video kids, I would use a star wars or marvel fabric, etc. This way they are unique (but easy on you!). With older kids I have often added a bit of mesh on the side to hold a water bottle.