let's break this down. it says:
i hope you have a good day. i hope you'll come back on chismas and you so silly and your tricky when we stay with you. i want to sleep with you not my dog becus he pups.
so, to recap: obviously, this kid has some sort of personal "sidenote" relationship with the soldier she chose to write to. i mean, the guy has stayed with them before. she knows him well enough to know he's "silly" and "tricky" and she, uh, well. she wants to sleep with him. but not her dog. because he pups, which i can only assume to mean poops. poor girl. she has no idea that grown men also pup and probably pup way more than most dogs. in some cases, grown men may also drag their butts across a carpet just like a dog if they're too lazy to replace the toilet roll.
hilarious. kids write the darndest, most unknowingly seductive things.