The cosmetics company Little BU have created a child friendly nail varnish which washes off. It doesn't state how easily the colour comes off but I can imagine it would be a bit of a pain if after one hand wash you as a mum were being requested to reapply another coat of colour!
Little BU Kyra Wash off Nail Varnish £9.95
Little BU Emma Wash off Nail Varnish £9.95
Little BU Riley Wash off Nail Varnish £9.95
Not a bad idea at all, but I would like to know how easily it comes off.