To answer your boy's query...
The donor mare (National Gallery) is served with the stallion's semen via AI.
The donor mare's egg is then fertilised by this semen inside the donor mare.
After 15 days with a positive pregnancy test of the donor mare the fertilised egg inside the uterus of the donor mare is flushed out through a filter into a petrie dish. The fertilised egg (foetus) located using a microscope (one of the most amazing sights I have been privileged, in my view to see) is then inserted into the recipient mare who will carry the foetus foal to full term and birth of a wonderful foal. The recipient mare then nurses and cares for the foal to weaning before fading from the scene so to speak.
The foal's breeding and DNA is that of the stallion and the donor mare.
Good luck in explaining the details to your son but that is the process of successful Embryo Transfer.
Cheers
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