We're getting ready to move my DS to a bigger bedroom and buy him new bedroom furniture. It's a very large room and I'm wondering if I should go for the full or twin sized bed. What size bed is your preschooler in? Right now he's in a toddler bed. I'm also considering a bunk bed, full at the bottom, twin on the top. But I'm thinking maybe he's too young? He'll be 4 in March. TIA!