How is a gerbil put down?

[Polyethyl]

I need to prepare my 10yo for tomorrow.
Our last remaining gerbil has reached her time, she’s suffering.
For a creature as small as a gerbil, is it an injection? Like with a cat? My 10yo is undecided about whether she wants to be there at her pet’s going, or if it would be too much for her.

I Googled this -

Sedation with an Anaesthetic GasThis involves being given anaesthetic gas via a small mask or inside a clear box, this method involves far less handling so is better for those nervous ones or those that become stressed. The downside is that due to the gases used, for your safety you cannot be present for this. The unconsciousness that occurs is very short lived so unfortunately the final injection needs to be done quickly, so often away from you as the owner.

Had to have dc's very old hamster put down a couple years ago. Was during Covid so I wasn't allowed in the room, however the vet said they would give it some gas to make it go to sleep and then inject it into the heart which they wouldn't feel due to already being asleep. I was rather glad my dc wasn't allowed in due to where they injected them, so maybe get your dc to say goodbyes at home first. I brought the body home and buried it in the garden and had a mini funeral.

Whiff of gas and an injection. The vets will bring the wee critter back to you afterwards, if you want then to, to say goodbye.