While it definitely depends on the closeness of the child, our general rule of thumb is 15 - 20 for both family and friends. It also depends on the gift I buy. I don't like to buy clothes or toys just to buy them. I try to get a gift I think the child and/or parent will really appreciate and use.
i think if you are not the childs parents and maybe notthat close - or the child has everything, a savngs bond is always a nice gift. the child won't remember you gift next week anyway, and this is a perfict opportunity to help there furture