I've built a loft bed for my 4 year old following the plans posted here:
http://ana-white.com/2012/07/plans/camp-loft-bed-stair-junior-height
I modified the plans slightly to use a ladder instead of stairs, and added diagonal braces in each corner to connect the legs to the side rails to prevent the frame from wobbling. The bed seems to easily handle up to 200 pounds, and everything feels very secure.
My primary question regards the strength of the pockets screws, which are the only joinery method used. Are the 2.5" pocket screws really going to be strong enough in the long run? I used 2 pocket screws on the end of each 2x4, and 6 on the 2x6 pieces. Should I be concerned about these eventually failing?