It would have been cool if they were on before. It would've been interesting if Angel encountered one normal family over the course of his travels, and they turned out to be the ones who looked after his son.
The only character like that in the Buffyverse is Ann/Chantrel/Lily. She started out as a vampire worshiper who Buffy & Angel rescued from Spike, moved to LA as a vagrant, Buffy rescued her again and inspired her to become a worthwhile person, and she wound up helping kids like her.
The only thing that bothered me was that she nor Angel remembered each other from Sunnydale. The fact that she remembered Buffy, but not the handsome man who saved her from the monsters seems a bit odd...