A character of any alignment could respond in any way. Alignment is a tendency, not a restriction.
Cruddles, my CG Deep Gnome wizard, would likely help the kid escape and leave a few coins.
Lex, my CG human monk (who is a tad crazy), would capture the kid, force him to be honest, and then buy the bread for the kid as a reward for being honest. He'd also protect the kid if the punishment would be too steep from the constables.
Myztek Dryken Delerosh, a LG fighter/wizard, a former CE Thayvian under a helm of opposite alignment, would capture the kid, hand him over to the constables and say the law is the law.
Tyrstern Fossilrock, Mountain Dwarf NG barbarian, would place a bet on whether the kid was caught and would otherwise stay out of it.
Kyrus, the Jack of all Trades Elf, NE, would either ignore it, or use the situation to force the kid to work for him.
Crynare, my CN mage/thief, would steal the bread because it clearly meant a lot to the kid. He stole what people valued most.
Myska Urge, CG tiefling ranger/fighter/rogue/sorcerer, would capture the kid and teach him the importance of redemption, compelling him to do a greater service for the world than the harm he had just done.
While some of those might fit into your definition of their alignments, some of it won't - and that is ok. They're all being played as individuals with personalities. The alignment assigned to them is just the best fit, not necessarily a good fit.