I want to redecorate my kid’s room.

Make sure you have a door in to the room, otherwise all your hard work will be in vain.

How about a spiked tiger pit in the center of his room?

Yeah, ask your kid what he/she wants..
As a kid my parents asked me and i told them i'd like Davy Crockett wallpaper and when i got it i was blissfully happy!

Yes, don't use a bed frame, just put the box spring and mattress on the floor, that way they can't hide anything under the bed.