If You Buy A Kid A Castle
He'll probably want to fill it with sand.
The sand will get his hands dirty, so once it's time to eat lunch, he'll ask for the hose to wash up.
You might have to step inside the house for a minute, at which point, he'll think it sounds fun to flood the castle completely.
Then, once he's nice and wet, he'll sit right down in the middle of the (once-sand-only) castle.
He might forget the rule about not getting water on the patio, but he'll manage to keep from falling and cracking his head open.
He'll need a place to rinse off from all of the sand / water castle fun, so he'll make a pool in his wagon.
While rinsing, he might forget the other rule about not standing in the wagon (and then stop to pose while you snap his picture).
He'll probably play for hours, happily, filth-ily running back and forth between water and dirt sources.
If you buy a kid a castle, he'll probably finish playing in it by asking you to take him to the real pool--"Now!"