That's a FASCINATING question! It made me curious, so I looked for previous studies on cultural differences in smiling among babies. It looks like there are differences, at least, in how often mothers smile at their babies. But I think it would be super-cool if someone eventually pursued the research question you suggested.

I didn't read the following study, but it's just an example I found of cultural differences in smiling at babies:

https://www.sciencedirect.com/science/article/abs/pii/S0163638312000410

Also, if you're curious about the piece I read that explained the prevalence of smiling in the US, I think it was in The Atlantic — but I can't read behind its paywall at this time to confirm. Either way... cool stuff. :)