If Family Guy wanted to do this premise, they had a built in backstory. There is an early episode where Peter knocks over every vile of semen in a lab and has to refill it himself so there is a reason he would have had all of these kids. They didn't need to make up a backstory about him donating sperm in college, although I guess that would explain their ages.
It had its moments, and it was something different (although not really original) for the finale. Family Guy has seen better days though.
It had its moments, and it was something different (although not really original) for the finale. Family Guy has seen better days though.