@dkeefe I think a lot of the idea that toddlers are better with family comes down to an assumption that either caring for young children is necessarily completely unskilled work or a rejection of the value of ECE education, with both tied into demeaning of "women's work" in general).
Would my dad do better electrical work on my house than a licensed electrician? Would my mom provide better medical advice than a doctor or pharmacist? They'd both be able to direct more attention to it if I wanted- is that all that matters?
Similarly, is my parents' house safer than a licensed daycare? Is my MIL as skilled at watching children as my daughter's preschool teachers who are both getting masters in ECE? And it never seems to come up that a SAHP of a 2yo might also be caring for newborn, sleep deprived, and exhausted when I'm sure my the teachers in my kid's daycare must have more energy than me at 40 and surely more than the grandparents in their 70's.
Another factor that never appears in these considerations is screen time, which is known to be a negative. But a SAHP of 2+ kids pretty much always resorts to screen time during the day and a quality childcare center will not do any. There is also a known achievement gap with children from poor families who are "watched" by family who sit them in front of the tv all day- the gap that is minimized by universal pre-k.
So basically the assumption is just because someone is your family, that means they are good at watching children.