Any roll-type bread, such as those meant for hoagies or subs will work fine. I've even been known to use hot dog buns, but hot dog buns do fall apart more easily.  When serving small children, I look for smaller rolls that will hold about 3 to 4 meatballs on each sandwich.  Smaller rolls help reduce the risk of spaghetti sauce-stained clothes (and spaghetti hair) since they're much easier to hold and eat. You could also just put the meatballs in a bowl and eat them with a fork. (Which is what I do when trying to stay low carb!)