sammy's was finished first (since it needed to be shipped to ohio) and i used ribbon ties on his. he also got a park with a lake that he could drive to and a store.
after making his and having a couple weeks of other projects in between, i decided to use something different to fasten the folded mat together:
aaron and oscar got tabs on theirs with velcro. i liked this solution a lot more, and wish i had thought of it the first time around.
he did notice there were two different ones, but figured that one of them was for sammy.