The only reasonable provision to make for the offspring of a creator is to extend the copyright term to a maximum of the creator's lifespan, plus the mean human gestation period, plus the age of legal majority. For the sake of simplicity, we'll just call it 20 years.
I'm willing to support a creator's minor children until they are old enough to support themselves. I am not willing to give them a free pass for their entire lives just because they were lucky enough to be born to a popular artist.
I wouldn't even let my own kids freeload off of me once they get old enough to leave home, and I actually like them.
Nor do I think that an artist should be able to make something while young, and rest on the same laurels until the day they die. Certainly, they should be able to retire at the same age as the rest of us, and expect their last work to remain protected until they die, so the regular term should probably be no more than the numbers conservative retirement planners use: the 95th percentile for life expectancy from age 65, or about 35 years.
So a maximum term of 35 years, and a minimum term of 20, with the term for works in between those ages ending upon the death of the creator. Works done for hire would simply have a term of 20 years.
That's very reasonable, in my opinion.