I agree with your post 100 per cent. The parents might still come back. If they don’t there are wild bird rescue groups. I would call one.
I say this because I tried to keep an abandoned martin alive. I couldn’t keep the little guy in grub, lol. I ended up taking him to a rescue group..they said he not only lived...he lived to fly away.
That’s great!
About a month ago, I got to see an abandoned hummingbird get adopted by a little mom that only had one egg hatch (they usually have two, the second didn’t make it). The rehab person handled the baby without gloves and good ol’ Phoebe just counted beaks, a little startled, and started feeding her new chick right off the bat. Her newest clutch is on fledge watch.