The more bare, the better. Children's feet are soft and pliable and their bones are still continuing to grow and form. Dr. Michael Nirenberg, podiatrist and Primalfoot Alliance Advisory Board member, says this on his blog about children's feet:

"Don’t be in a hurry to buy shoes for your child; wait until your children begin to walk, usually at 11 to 15 months of age. Even then, the MOST IMPORTANT THING TO DO IS KEEP SHOES OFF YOUR CHILD’S FEET AS MUCH AS POSSIBLE.

I cannot emphasize this enough! The best “shoes” for your children is no shoes!

Allowing kids to walk barefoot on various surfaces, especially mildly uneven ones like you find in most backyards, fosters development of their foot’s muscles, ligaments, and balance."

Putting shoes on your children's feet too early or too often sets them up for foot ailments later in life. The best course is to let their feet be feet first.