Firstly, I don't see tje problem with this, as long as the parents give consent. I think that we should be burning all waste, even the excess heat resulting from normal cremations, used in heating buildings, water etc.
Secondly, in Denmark this sort of thing has been done for a little while. In the last year, the first heat exchanger using excess heat from cremation was approved, the heat then presumably being used to either generate electricity, or to heat water. In Denmark, they commonly have something called district heating. We have it here, but it's not widely used, but is becoming much more common in new builds.
Basically, when you generate electricity, a lot of heat tends to be produced. For some reason, in England at least, we cool the water vapour that was created in the process down, and outlet to the atmosphere. In Denmark, they use this excess heat to power generators, or it is used to generate hot water. This hot water is then pumped directly to your home, and you get instant, and clean, hot water via another heat exchanger, which is a source of clean water for domestic use. By doing this, they've reduced the amount that energy generation costs. They do, however, pay very high taxes on energy to pay for welfare.
It's a very good system, if you find the tax acceptable. It's an expensive country though. Anyway, the Danes have some excellent methods of saving energy, and the use of excess heat is one of them. Why waste it?! Which is why I'm in favour of this.