In the matter of gifts generally the law does not look upon gifts with any great favour, especially if they tend to impoverish the donor. Replying to your specific questions, in the break up of a relationship (of whatever nature, whoever broke it up, for whatever reason) then each must return gifts (because they are conditional gifts - made in expectation of the relationship continuing - as my first answer). Often in determining what is whose it is simply decided by who paid for it. If the boyfriend gave gifts to the girlfriends children (irrespective of who is the father) it is assumed that the girlfriend influenced the boyfriend (by allowing him to think that the relationship would continue) so therefore the gifts are conditional and must be returned to the boyfriend at break-up. Hope this is clear, but if not please ask me further.