Re: IKEA kura bed...what age?
My girls have it. They probably got it about 4 or 5 months ago, at 2.5 and 4.5. The 2yo sleeps on the bottom, but she does go up onto the top one to play sometimes during the day.
Really I think it depends on the kid, my older one is up top and she is a pretty heavy sleeper and does not roll around a lot so it does not worry me. My 2 yo is an amazing climber and cautious so I am also not to worried when she does climb up there. Use with the recommended mattress and I would say your 3yo will probably be fine up there. If you plan on using the underneath bit currently, build it as a little reading nook with some cushions etc... i think it would be really cosy! My kids love to hang a blanket from the top one and have a 'house' or 'boat'.