When people talk about their kids' age, it's usually in months. Children's clothing is sized according to months. Their well-baby visits occur at certain monthly intervals in their development.
Julia has been alive for 29 months and Avery for seven.
If adults thought similarly about age, we'd be a heck of a lot more depressed.
I am 399 months old, weeks away from 400.
(I don't even want to know what sized clothes that would make me!)