Not advice exactly, but three mistakes I made that might help someone down the line.
If you have youngish children:
1. Listen to your inner voice. If something snags at your subconscious, even if it doesn't make sense and you don't know why, stop and work it out.
2. Have a recent, good quality, photo of your child.
3. Have two phone lines open and agree a protocol for using them.
Backstory:
Daughter is in running club. Training on a Sunday is in park a few miles away.
I drove her over, pulled up and saw some green tabards (club colours), dropped her off and drove away.
Half way down the side road from the park, something niggled my mind. I stopped, but couldn't work out why and drove off.
I got home. The niggler hadn't gone away. I had a cup of tea. I looked in the diary - no training. Bugger. I drove back.
Noone in carpark. Noone in sight. I rang daughter's phone. No answer.
I rang home. Daughter's phone is at home. We agree that she's probably caught a lift back with a friend (others had turned up hence the green shirts).
I go home again.
A while passes. She's left her phone at home, but probably friend is dropping a series of kids. We call likely friends. Nobody has scooped her up, but one family saw her.
I go back to the park. No one around. I call home. We agree to call the police.
My partner calls the police - and is asked "has she ever gone missing before?" - no; then "do you have a high quality recent photo?". They're putting all cars out and calculating an expanding drive-radius. It all gets very very real in an instant.
I'm unaware of my partner being floored... because she's on the landline to the police and her mobile is on silent. I ring and ring and get voicemail. I need to ring, because I have found daughter.
In the saeconds after being dropped off, daughter had spoken to mates and found trianing cancelled. She tried to catch up with me as I drove off. When I stopped halfway down the lane, she almost got to the car... but then I pulled away and didn't notice her. she was upset by this, and walked into the fringes of the wood to hide her tears and wait the 2 hours until she thought I'd come back. When I did, she was looking the wrong way and didn't see the car, and I didn't see her.
I called the police directly to tell them all was well, but they said they couldn't contact the team that had by now gone to my home.
Finale is that tearful daughter and dad run into living room where 2 PCs are getting details and consoling mum.
A phone at home. A phone on silent. Looking the worng way. Not checking the diary. Not listening to the inner voice that remembered the cancellation but didn't poke it into consciousness. All trivial stuff... but easily the most terrified I've ever been.