Children generally grow quickly, so they often don’t wear down their shoes before they outgrow them. There is one big exception to this rule though: play shoes — shoes which are pulled through the mud, jumped on and dragged along on bikes. These shoes get worn down, especially around the toes and the heels, in the blink of an eye.
A friend of mine recently reminded me of Shoegoo, a genius product that the skater boys I lusted after in my misspent youth used to use all the time. It’s a gel that you spread around the used toes or heels of the trainer. Overnight it hardens and builds a protective new layer around the shoe. It does not make the shoe look “as good as new” but beaten up play shoes are given a new lease of life and it beats having to buy new shoes every month.
You can pick a tube of Shoegoo up from most skateboard shops, all over the world.