What is the best footwear for children?

I was at wal-mart yesterday and was noticing the different types of footwear the children were wearing. I usually don't notice this stuff, but yesterday I did. Amway some of them were wearing sandals, some flip flops, crocs were common and some were wearing tennis shoes and socks. I noticed the kids wearing tennis shoes had the most natural walk while the other footwear mainly flip flops seemed somewhat restrictive. In other words you can tell that their not wearing regular shoes without even seeing their feet. It seems to me that tennis shoes are best from what I seen and from my own experiences. What say you?