I'd like to think that none of my kids would come up with such a wild idea, let alone try to implement it. In todays world it was probably a small miracle that the kids were stopped and didn't end up prey to some depraved kidnapper.
To answer your proposed question, 5 and 6 is definitely too young. I'd say twenty somethings are best age for marraige.
Now that's funny. I wouldnt have been laughing if it were my kids that went missing, but those parents will laugh about it too. Probably already are. It would never have worked out anyways, another few years and he will be in that "i dont want anything to do with girls" stage and she'll be in that "too cute for any boy" stage...... Oh the life of a child.
To answer your proposed question, 5 and 6 is definitely too young. I'd say twenty somethings are best age for marraige.