Being born in the winter is a risk factor for schizophrenia. Kids born closer to the end of their school year are more likely to be diagnosed with learning disabilities early in life since in preschool/kindergarten a few months are still significant in terms of development

You may be interested in a Epigenetics It's a scientific field that studies environmental influence among other things.

I wouldn't be surprised, but I haven't heard of any positive results like that.

One thing is that kids that are born near the beginning of the year tend to have an advantage in school and sports, being older than other people nominally in the same age group. You notice a lot of January birthdays in top athletes. That has more to do with human systems derived from the seasons though.

Somewhat related, I wonder how much of an effect birth month can have on a child's school performance, social development, and athletic ability.

Where I live, a child is eligible for junior kindergarten starting in September of the year they turn four. A child born in January would therefore be around 56 months old on their first day of school. Meanwhile, a child born in December would be around 45 months instead. That is a substantial gap, and my experience with kids that age is that even a difference of a few months can see dramatic changes.

I'm personally thinking right now of my nephew, who starts JK in a few weeks. He will turn four right before Christmas, and when he returns from holidays, some of his classmates will start turning six because he'll be in a combined JK/SK class. I can't imagine how difficult it might be for him to keep up with those much older classmates, a situation caused by virtue of his birthday.

A child born into winter will experience summer soon enough unless something bad happens. I'm certainly not an expert on babies and their development, but I'd think it matters little. A more interesting topic might be the pregnancy - fetal development sets the course for the next few years or even decades, I'm thinking about epigenetic imprinting. That would certainly have an influence, but since we do not have mating seasons (well, spring and december maybe) I'd wager the impact is comparably low.

The thing is that the signs should now include a 13th to account for the procession. The whole thing is bs to me.

Possibly, though seasons vary wildly across the earth, so results would likely be limited to regions, and even then, we travel around a lot and have things like electricity and indoor heating which would probably negate most impacts.

Maybe but there are tons of other factors too and honestly we don't know yet. But the astrologers neither.. So no, no connection with astrology which is just a guesswork.