Why can the embryonic stem cells convert into various types of cells? where are the very first gene( to make it differentiate) from within the embryonic stem cells

Because they have the ability to be any cell and they haven't become a designated cell yet.

That is

If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other.