We have kids too. We use "Computer" which is one of the wake words offered by Amazon because we don't want our kids to get used to the idea of bossing around a person.

Also, I've mapped all of the functions we use to "recipes" that include the word "please" so that they don't work unless you use the word "please." i.e. the upstairs lights are named as for example "the Chicago lights" and there is a recipe that says "turn on the Chicago lights" when someone utters "Computer, please turn on the upstairs lights." So if you say "Computer, turn on the upstairs lights" it says "I don't know what upstairs lights are."

The disadvantage of this approach is that you need to get the string exactly as stored.