The synchronisation works automatically. However, you may have to synch the balances manually by swiping downwards in the transaction report view in the app.
If this does not work, something might be wrong with the synchronisation. If this happens you might need to delete the connection to the bank and "start over". To do this, go to Settings → Connect child’s bank account and click on the little red trash can next to the account. Please note that if you have more than one bank account connected, you need to disconnect all connected accounts.
If the problem persists, please contact our support team.