I demonstrated technique for my students with an seven year old girl as my partner. I showed them that I could be gentle and effective. Now, when my students start to get a little rambunctious, I smile and say "Seven year old."
In my opinion, aikido isn't for being tough and taking on all comers. It's for dealing gently with a kid who's having a tantrum and lashes out at you, or with Grandma when she's off her meds.