Sharing a Kid's Room in 600sqft ( part 6)

I am incredibly appreciative for all the comments and suggestions on my previous post (click here) about how to configure the shared kids room.  Your thoughtful responses are helpful and opens my mind to concerns I haven't considered or new ideas I haven't come across previously.  It's inspired me to search for even more alternatives for their small shared room. 

One great idea offered in the comments (and in Em Morrice's Interview Here) was for a trundle bed.  A twin trundle would address two issues. Firstly, at 3.5 years old, Theo is not recommended to be in a loft bed or bunk bed by any manufacturer.  We worry about him falling out at night.  Also he is a bit of a monkey and loves balancing and jumping and we worry about the sort of acrobatics he would attempt on a raised bed.  A twin bed that he could grow into and a trundle bed for Mae could be a great alternative for keeping him safe and still allowing for play space in their small room. Also I love that if things changed and we gained another bedroom we could use the trundle for under bed storage or as a bed for sleepovers with friends.

The downside I see for a trundle bed is that it may be tedious or difficult to pull in and out every day.  I'm also a bit cautious about putting Mae on a trundle bed before she is ready.  And by ready I mean, able to understand that she is to remain on her bed and not crawl/walk out of it.  We didn't move Theo to an open bed until about 2.5 years old.  The transition was really smooth but not sure if that is attributed mostly to his age at the time. 

Anyway, I'm adding it to the list of options.  There are many trundle beds on the market but my top choice would be the Oeuf River Twin Bed.