This very much depends on your child's birth order! There is no cap/maximum amount that you can put into the account, but the government will only do a 1-to-1 matching for the first $3K that you deposit.
Meaning, you'd be able to get $3K from the government when your child is born - and up to another $3K based on how much you deposit. If you deposit $3K of your own money into the account, you'd have a total of $9K inside (initial $3K + your $3K + government's 1-to-1 $3K). If possible, that's the best possible scenario!
It doesn't "stop" - when your child turns 12 years old it'll become what's known as edusave, and then a post-secondary savings if your child still has balance by the time he/she finishes secondary school.
Of course, don't deposit everything you have because it's not withdrawable as cash - so make sure you have enough to sustain family living before you make any deposit!
Here's a more comprehensive article about CDA accounts:
https://www.dearlittleones.com/single-post/2018/05/17/Managing-Your-Childs-CDA