Possible. I've heard of cases where police were not called immediately, and it seems to always be a reasonable explanation.
I can tell you that nearly 25 years ago, my son wandered out of our yard while my back was turned and to make a long story short, he was found an hour or so later, more than a mile from our house, in a pasture with a herd of cows around him. He was almost 3 years old. We never did call 911. His dad is the one who found him. If he had not been found when he was, we would have called the sheriff's dept and they would have come out and searched on horseback, but my husband's instincts were good and he knew our dog was with him and that our son loved to explore the woods and creek banks. If something terrible had happened we would of course have been kicking ourselves for not calling them, but we were very lucky.
There are probably many cases like ours where children are found without the help of LE. Sadly, some are never found even WITH their help. There's no way to explain it, but I thank God every day that our son was okay.
ETA: I have to reclarify.... he was actually found within about half an hour or so, but it took at least 20 minutes or more to walk back to our house with him on his daddy's shoulders. But I knew the moment when he was found because the calling his name stopped and everything was quiet.