Shared iPhone for 2 kids

[dag15]

I’m in a family of 4 (2 parents, 2 kids). My wife and I want to repurpose an old iPhone for the 2 kids to share for occasional use (Having a phone at practice, out with a friend, etc). For now this phone number/iPhone will be for either kid to use when needed. The iPhone will be limited to phone calls, texts, and some other basic apps (I realize I can use parental controls relatively easily from Apple ID/Family sharing). Our current Apple/iCloud family account has 3 members (1. Organizer, 2. Spouse/parent, 3. Kid A) The two kids share an iPad using Kid A Apple ID. Eventually both kids will have their own iPhones/iPads/Apple IDs. However, for the time being what would be the best way to manage the Apple ID situation for the shared/parental controlled iPhone? I see several options, but maybe I’m missing something.

1. Use kid A Apple ID. I don’t like this option because as far as I can tell through iCloud Family I would have to manage the Apple ID, not the device. I want to manage the iPhone very differently than the iPad
2. Create kid B Apple ID. I don’t like this option because kid A content (mostly iMessage) gets lost.
3. Create kid C Apple ID that is more neutral and won’t be used for any iMessage outside of immediate family/close friends
4. Go with some other third party/paid type of MDM. I really don’t want this option.

I realize the Apple preferred option is to buy/repurpose an iPhone for both kids. That will happen eventually, just not yet. Thanks in advance for any suggestions!