I don't think you have to owe anything to the children. Unless they found out that they were the result of a sperm donor, then they'll probably embark on a quest to find their biological father.

Sometimes it's the children that won't be traumatised, you'l probably find yourself in a sensitive phase about it at some point. But at the end of the day it's a good cause.

I think it's wonderful that you want to do this.