There’s a lot of underestimating going on—from everyone. The crisis prevention line, the cops, the headcount, the burglars and how “stupid” kids are, the scary guy next door, whether or not the scary’s guy son will welcome him home, whether or not Kevin can take care of himself (he can), Candy and his “bums” who aren’t there for Christmas, the stopping distance required to avoid hitting the lawn decoration, the cheapskate who didn’t leave a large enough trip, the amount of time it takes to make their flight, the value of a watch that looks like a Rolex, the amount of money needed to pay for 12 pizzas, the reality of Kevin’s house party, and eventually whether or not two crooks can beat a kid, and when they think they have him beat in the house he set them up in.
Also, the kid and the neighbor have one thing in common: they’ve both been physically abandoned by their families. And they both have different approaches towards facing that abandonment. (Though eventually one adopts the others approach).