Puppha's situation is obviously very sad and there are a lot of difficult issues to work through. I haven't the skill to offer any specific advice, but I thought I would just share what happened in my family on Sunday as a way of addressing the underlying theme of children in "mixed" families.
On Sunday, our daughter Mai, who is four this Thursday, attended the local cathedral with her mum as usual. It was Pentecost Sunday which commemorates the descent of the Holy Spirit to those apostles who Jesus left behind. I don't think she understood much of the finer points of theology, but she gets the general message that even when people have gone away, it is not the end of hope. That there is something bigger than our attachment to people which we can meaningfully relate to. And she also made, in the creche, a nice cardboard crown with paper flames which represent the Holy Spirit. That done, the family caught up with me - I had cycled to the local monastery for their Wesak celebrations. Mai turned up as I was circumambulating the Stupa with the monks and the other lay supporters, and so she joined in. Fascinating stuff! Ajahn Sucitto's chanting is quite impressive. I think she liked the idea that baby brother was excluded because he might poke himself in the eye with the incense offering, but mainly she just liked the calmness and solemnity of it all. She stood quietly while I made my offering, and then we all stood in the sunshine around the stupa for the Paritta chanting. I, of course, tried to focus on the Triple Gem, whereas she sometimes tried to stand on one foot, or tried to catch the eye of the friendlier-looking monks so she could smile at them. Later, time for chasing baby brother around the bamboo grove and relishing all our friends telling her how much she has grown.
Thus, Mai learns that there is much that is utterly beyond our present understanding, and that adults do some really odd things. But if you keep an open mind, and join in a bit, and copy the more relaxed and dignified in one's world, then things are nice, and there is not too much to worry about...

probably means the same as 'brother in christ').