Outright impossible to do with the demands of employment these days - young people are expected to go wherever the jobs are, they cannot stick around in some backwater rural town to take care of their parents. Not to mention that people these days don't have anywhere close to enough children, and it's pretty immoral to force people to breed like rabbits for their retirement.
Children sticking around isn't the only option. My mom intends to follow me once I've found a place to settle down in the next few years. I'll give her extra money which should allow her to live quite well on top of what she has saved and she's already expressed interest in helping with grandkids if I have any (I probably will at some point).
Obviously this plan is made much easier by remote work and good earning potential for tech workers and I suppose some parents will be more attached to where they currently live than my mom is. But multi-generational is not outright impossible, I'd wager a significant chunk of the population could pull it off to varying degrees in one way or another.
