I agree with kwinkunks, one can't give a specific response without knowing the kind of rock, age of the rock, whether there are other depressions/imprints of comparable size in the adjacent rock, etc.
In general, whilst there is a feint possibility of preservation of a human footprint in very young rocks, it is wildly improbable. Consider the surface area of exposed rocks on the Earth, and the trillions of impressions from differential weathering, a host of diagenetic processes, heterogeneous rock textures, etc. It would be very strange if, by chance alone, some of these depressions didn't resemble a child's footprint. But please try to give more details so can we can evaluate this inquiry.
Incidentally, this brings to mind some creationist 'arguments' for human and dinosaur footprints in the same strata. They have all been investigated, and all shown to be spurious.