This is terrible advice and I hope no one takes it. You'd generally never give a child permission to use your gun and if they somehow do get a hold of it and shoot themselves or someone else, what do you think happens? In several states you can be found criminally liable if you didn't have that weapon "secured" under the legal definition of the law.

In California all guns sold need to have a "gun lock", they are always cheap Chinese made garbage locks like this one, there are "secure storage" laws in California as all. In Massachusetts I believe you need to have a specific in-chamber lock and the most common lock sold was defeated with a ball point pen on this exact YouTube channel. They are 100% for liability, and offer marginal security.