At the moment, only one parent/guardian can be the account holder that the Kids Card and app is linked to and therefore be the Jar owner and have full control over their Kids card and their card linking.
However, you can share the Kids Card Jar with the other parent/guardian. To Share a Jar, tap on the Jar and then on Invite. You can then choose to Invite sharers from your Contacts list or someone nearby (if you both have your Bluetooth switched on) or use a QR code.
From there, the other parents will see how much your child is spending and pay into the Jar.
You will be the sole owner of the Jar, which means the spending limit will be set for the other parent/adult they are sharing that Jar with (e.g. the spending limit from this Jar). Alternatively, you can link your Kids Card with a shared Jar created by the other parent; in this scenario, they will be able to set the permissions.