Ok, I must say that I put that rule in from another RKC that someone had made, I guess I assumed they had play-tested the scenario so I did not do it myself.
I will test to kill a child sim with the Nraas mod that I use, and see how this works out.
I will have to play-test also without a mod. Sticking in a sim into a household gives the household new funds, which can't be done, this to keep the whole economic balance in the town. I see if I can think out a solution. The whole point of getting your children sick and dying is that it will be a disadvantage for the family, not the other way around.
Thanks for all the input Seera1024 and Kimeleon :)