Welcome fetal alcohol syndrome into your neighborhood.
I can’t see making this illegal. OTOH, I’d say you could get in SEVERE legal trouble for selling cigarettes or alcohol to a child.
But...
1. Why can’t a bartender (personally) refuse, or a bar refuse to serve alcohol?
2. And then if they do, the bartender and bar management/ownership is absolved of any responsibility for the child. I’ve learned (not the hard way, fortunately) that the ONLY time it is safe to ask a woman if she is expecting is if you personally see the baby crowning.