If your child is saving up for something big you can help them to avoid dipping into their pots every now and again by changing the settings to prevent them from removing money. Your child will still be able to add money, they just won't be able to transfer money out.
Tap on your child's name on the family dashboard
Tap on the Save pot or your custom pot
Tap the pen and paper in the top right corner
Toggle on/off the setting 'Allow [Child's name] to remove from pot'