Mrs Katz,
I will go out on a limb to say that as long as they were In the Gan (I guess until Motzei Shabbos) they didnt need shoes but once out of the Gan they needed shoes. Im guessing in the Gan the ground was soft and smooth but outside there was rough ground and thorns and whatnot due to the klalah that Hashem cursed the ground due to Adams aveirah.