All of my banking apps, among others (e.g. password manager), include options for both pin and touchID auth. Do we not already have what you’re asking for?
I think he's requesting it on the system level. For example, if iOS allowed you to force PIN+TID when opening a specific (not necessarily secure) app for the first time after an unlock. Intended for apps that don't necessarily have security built in already.
This is especially useful for when the app developer doesn't think there is a reason for them to develop such a system. For example, I don't want my son playing a zombie game, but I myself play it often. I could then lock him out of said game, but still give him my phone to use.
This isn't exactly what you are looking for, but have you tried Guided Access on iOS (or whatever the equivalent is on Android)?
Yes, that is the way I do it currently. It's a real pain though.
Which password manager are you using? 1Password doesn't support TouchID + PIN on iOS, but I wish they would.
I'm using LastPass on Android, and I have it set to require both my fingerprint and my LastPass password.