Over the summer, we took quite a few day trips. For every trip, I was outnumbered. One adult and 3 kids, sometimes there were 2 adults and 3 or more kids, either way, the kids had us beat. I couldn't keep an eye on each kid all the time and I didn't want to loose anyone. I also didn't have bright neon matching shirts for everyone to wear so we'd stand out in a crowd and be easily found it someone strayed. I also didn't think about this until I arrived at our crowded destination. Since I usually have my camera with me, I decided the best thing to do was to take a picture of the kids. I made sure to take a full body shot so I could see what they were wearing.
When going to a crowded place such as the zoo or an amusement park, take a picture of the kids so you know what they were wearing and have the picture on your camera or phone to show others in the case of a lost child.
Luckily no one got lost so we never had to show the picture, but I felt safer just knowing I'd easily be able to help others look for my lost child if need be.