How about a tactical wheelbarrow to carry everything in?
Looks like we all have different definitions of "Survival" and the time frame in which the child will have to survive.
The basics can be carried in a pocket. As you add items, you add weight, bulk and get further from survival supplies and drift in to camping/ living supplies. For 5-7 year olds, a little fanny pack or very small rucksack would work. at that age, they're just not going to tolerate humpin' a 15+lb rucksack while playing or hiking in the woods.
How long would a 5-7 year old kid be expecting to be alone? Probably have a full scale S&R going if it lasts beyond 24 hours.
+1 on the tactical wheelbarrow.
They need water, whistle, light/strobe. Toss in a poncho and mylar blanket and you are pretty much set. A food bar won't hurt and a small mirror could help signal the airplane that will be looking for them.
I could get on board with the personal locator beacon but as mentioned before if you lose a 5 - 7 year old in the woods make sure they are trained to stop and wait for rescue because within 24 hours the woods will be crawling with search and rescue and it helps if they haven't walked 5 or 6 miles in a random direction.