What is the ruling on a wife demanding from her husband the children's money that the European government deposits into his account instead of hers?

The determination of the rightful owner of the money refers back to the granting entity:

If it designated the wife: then it is her right, and the husband is not permitted to take anything from it except with her willing consent.

If it designated the child (which is the default): then it belongs to him, and his father must spend it for the child's benefit, in his capacity as the child's legal guardian.

A father's disposal of his child's money for his own benefit requires elaboration.