Sweet as molasses, Lisa. Well written,too.

"Shared blood" seems mildly awkward as written. I like the chorus, but could not come up with a head tune, but I'm no musician, so, there you go. I DID do a quick re-write to make it fit the tune I hear. Should I show it? Oh, I don't want you to take it like I think it's an improvement. It isn't and I don't. OK, here.
Only Child of mine
I'm sorry if you're lonely
If only I had seen it then
A brother as your constant friend
And someone you could count on, too
Or sister who could soothe your fears
Each time those solitary tears
Turn your little world to blue

I think it's a great topic, unexplored as far as I know. Best to you in the New Year (and to that only child of yours). Guess he already has pet(s)? There's always adoption and you can fit the age...just don't think Russia...