Stages of acquisition of dynamic balance
Before age 4, kids need to learn to direct their bodies in a given direction in order to gradually narrow their movement while moving both feet side by side.
At age 4, kids can walk with one foot in front of the other, alternating them, on a support that is at least one and a half feet wide.
At age 6, kids are able to walk with one foot in front of the other, heel-to-toe, on a support that is at least the width of their foot.