I posted before seeing yours here but it really comports with what I believe to be good parenting, and you also gave some good rationale, such as regressions and change of school. Young children absolutely respond in drastic fashion to big changes, sometimes good and sometimes bad.

And societal norms are huge too. I always joke that there’s no pressure quite like peer pressure, and that a child who’s maybe a little delayed in their maturity will have a fire put under them when they see themselves getting left behind by their peers. I had my kids in daycare from six months, because I fully believe that being surrounded by members of your cohort is hugely important in development. On the first day of public preschool, you can tell which kids had some form of daycare prior and which kids spent the last three or four years with mom, dad, or a grandparent.