Is it permissible for the mother to take a portion of the social security allocated to her 10-year-old son, given that she is married to another man and the son lives with her?

The maintenance of a young child who has no wealth is obligatory upon his well-off father. If his mother spends on him—not as a donation—then she has the right to reclaim it from the father. If the mother is financially secure, she is not permitted to take anything from the child's money. However, if she is in need, she may take from it what is reasonable.