I would go with biometric because your kid\s aren't going to guess the combo(watch over your shoulder) or find the key because your fingerprints are the key. As mentioned above this is no replacement for " a proper early education in safety and respect"
I am currently looking at safes myself and have found Pioneer Safes on ebay. The guy who sells them lives just north of Ft. Wayne and use to own Liberty Safes. I have not found any negativity about them aside from the "Made in China" aspect in my research. Also for me I can pick it up and save a little more money since I am pretty close. May want to look at them to. Guys name is Marc. Just my .02