water gun
water pistol BrE

She felt stupid, like a kid with a water pistol.

Anyone else here would know it was a water pistol.

He seems to be from the military, and fights with a water pistol.

It was a child's water pistol made of transparent plastic.

It could be a water pistol for my kids - I'm always playing with those.

Out of the bushes jumped a young man with a water pistol.

In his huge hands the nozzle looked like a child's water pistol.

"What are they going to go after next, water pistols?"

He still had his gun but it was no more use to him than a child's water pistol.

He was the only boy who didn't have a water pistol.