I love the account for my daughter. I don’t want her to have a phone tablet of her own but want her to be able to see her balance, and reference it against saving goals. What I’d love is a connected screen/piggy bank etc that always available for her to check.
You want a connected screen but not a phone or tablet?
You could knock up a Home Assistant instance running on a raspberry pi with connected screen/e-ink display which displays a 
Personal account balance - but the Monzo API unfortunately doesn’t support Child accounts in this way*
*At least the last time I tried it when Child accounts launched
not sure what screen she is using to look at this but just create a basic web page and manually update it with what her balance is whenever you add money/you get a notification money was spent and she can sit and stare at it all day long