Strongly re "国内很多人都不把这个当回事儿,你就是说了孩子什么不能吃,有人可
能也没往心里去。" especially old people.
My mom has a college degree and has the following deductions:
Since she hasn't seen or heard of any kids with allergies in China
throughout her life, it means that probably kids would not have an allergy
issue in China even if they have allergies in the U.S. It's not about the
people, it's about the land.
I'd recommend against bringing your kids back to China since they'd go to
daycare shortly.