This was entirely for their own benefit. They probably figured someone would have eventually identified them from the porch cam footage once it was revealed that the footage existed and so they gave the thing back and acted all sorry. Bullshit, they're probably just hoping the kid's father won't press charges since they were nice and returned what they stole. I'm also guessing they used the media as a springboard to tell everyone they only stole because they're homeless in hopes that someone will shower them with kindness for their "kindness" of returning something that they fully intended to keep and sell until they knew it was meant for a very sick child.
You think they would have given the belt back had it been taken from an adult's porch or was stolen from a healthy individual of any age? Or had the dad not pissed and moaned on the news about it? I'm gonna go with "NOPE for $500, Alex." Sorry Moo, but even if you gave it back, you still not only stole someone else's stuff, you stole their mail. Congratulations, now it's a federal offense punishable by up to five years in prison? I sincerely hope she gets charged with something to make her ass think twice about stealing people's packages.
Tons of people have porch cams now for this precise reason and it'd be wise to assume that any given porch is under surveillance. If you don't want to get raked over the coals for taking things, don't fuckin' steal shit off people's porches!