You can have your child use the default profile, and have a shortcut whose target is `firefox -P <adultprofilename> --no-remote` somewhere out of her way. This way, she can just open the browser and use it (on the default profile), and you can click this shortcut to open your profile easily.
Just an option to keep in mind in case you decide to get rid of Chrome in the future.
yeah but the scenario is really, dad is on computer, dad goes in kitchen to make food, child goes gets computer, opens new tab in running browser.
It's really a parenting issue, I could stop her doing it but I don't care enough to do so, and if I don't stop her via parenting there will always be ways she slips through the profile guards.
Just an option to keep in mind in case you decide to get rid of Chrome in the future.