How does the savings interest work?

You set the rate — there is no rate of ours. It is paid monthly on the savings balance, and you can set a different one for each child.

There is also a fixed deposit with its own rate, for 1, 3 or 6 months — broken early, it gives back what was put in, with none of the extra — an optional parent match on what goes in, and an auto-save slice of every payout. All of it is yours to set, on Settings → Investing.

The parent match is only paid on savings above the child’s best ever, so money taken out and put back does not earn it twice.