if still alive after the crash, is not able to escape a fire, or to look for help.
Valid point but it's a risk not unsafe. There is a difference
In addition you cannot really affirm he agreed to take such a risk. If it were you own kid it would maybe be different...
Personally my daughter does not consent to anything. I'm the Dad and my word is law. I determine what my daughter consents to until I'm convinced she has the judgment to do so on her own (probably somewhere around her 42nd birthday) That said a child should not be taken up without parents consent. If a parent consents then it matters zip what the child consents too. Parents are the boss children are not.
Meanwhile I am also quite sure single piston engines crash very regularly...
really? I think that is a false statement. I'd say even single engine aircraft crashes are not very regular. They happen but it is hardly normal
What does the father think about it?
I would assume if the child is in the plane the father or mother should be well aware of where their child is.