I don't know about "fat" but certainly anything that involves being active and shoeless will result in a natural "splaying" of the feet. I thinks it is a GOOD thing to have that time to explore proprioception without shoes - better than all the sports and exercises that people wear special supportive footwear for - because humans were meant to walk and run and jump barefooted and experience their relationship to the rest of the world that way.
l ya know I keep trying to explain the same thing to horse owners regarding horse shoes. And the cool thing is that very often horses feet do expand and get larger when they are taken out of shoes and allowed to develop a healthy bare foot.
Surefooted increases, tripping decreases and the whole mechanism of the foot becomes healthier. Of course all of this takes time. now you got me thinking barefoot is not such a bad thing for us humans as well.