I have 5 iPhones on my family share account. When I check the detailed messaging history on my son's phone, it doesn't show where I had texted him from my phone and visa versa. My history doesn't show texts to or from him. Exchanges between me and my wife show up in my detailed history but texts from me to our sons or from my wife to our sons don't appear in our history or theirs. Any ideas?
Are you and your son using iMessage? If so, those will not show up in the messaging history as they are counted as data an not as individual messages.