Saikat, not sure if this is very useful, but this equation gives a ballpark estimate of preferred stride length (SL) as a function of walking speed (v) and leg length (L):

SL = 2.5*L*(v/sqrt(g*L))^0.6

where g = gravitational acceleration. The original reference is Alexander & Maloiy (1984) in Journal of Zoology and you can find a more recent use of it in Srinivasan (2011) in Journal of the Royal Society Interface.

Not sure if it is valid for children.

Hope this helps,
Ross