Check your states nuisance animal laws, you may be able to switch from a water pistol to a pellet gun or bow.
And you can sell squirrel caps to the neighbors' kids.
Having said that, I tend to lean on the side of the other poster in that harming animals should be avoided unless there's a specific reason (such as eating them)
At some point the world isn't kumbaya and the animals will learn when they tend to die or be physically hurt when approaching that activity.
Get yourself a good, sharp paring knife or pocket knife and some kitchen shears and you're good to go.