I also like play pens. I have two here who co-sleep at home, and will not lay down unless a parent is with them and/or they are nursing. Here, they go into their play pens quite happily. I have the younger one (1.5 years) in a sleep sack so she won't climb out. The two year old has not tried to climb out yet, but I am concerned that he might. I guess he'll go into a sleep sack at that point LOL. The fact that neither child goes to bed at home without nursing, or at least a parent going with them means I doubt they will simply stay on a mat here.