Sounds like MediCal would be the same bucket as MassHealth.
If they're new enrollments in MediCal, I can see how that could be a result of the ACA marketing for individuals to obtain health insurance, and utilizing the national website (when it's up) to get to the MediCal website. But, I agree that it's shady and definitely a stretch as far as statistics go, and should be in it's own separate reporting caveat.
ACA allows children to be kept on their parents' insurance up to age 28. Depends if you claim them as a dependent on your tax return. I assume at age 4, they're still your dependent, and don't really need their own work. But, if you're not claiming them as a dependent, I guess they would qualify for MediCal.