You can always call your insurance company directly at the number on your card. If you have Blue Cross Blue Shield through Anthem, this could be a result of the massive data breach. If you have been dealing with a particular insurance company routinely for your child's healthcare, it is not very likely they need to verify their year of birth as it would already be in their records and on any claims filed for their care.
The attackers are going after kids, because its unlikely that a child's stolen identity will be detected for many years. I got calls from them back in early April from other numbers.
Anthem Healthcare has set up a website and will provide current and former Anthem customers with free credit monitoring for two years.
Go to https://www.anthemfacts.com/ for info and to request credit monitoring.