... are/were they breast or bottle-fed at the time?
Dh has a theory that breastfeeding delays teeth so I'm wondering if he is correct.
So:
dd1 - first tooth at 7 months, bottlefed from 6 months
dd2 - first tooth at 6 months, bottlefed from 2 months
ds - 9 months, no teeth yet, breastfed
Add your details and I'll work out the stats!!