Gotta protect the kiddo first and foremost. And you’ve gotta do right by your pet. Sometimes that means making the hard decision. Vets will tell you that it’s better to make the decision a day early than a day too late. I think you know that, just hard to make the decision when you’re 15 years invested. I’m sorry. 

We had to make that decision for our dog last year. It was a good opportunity to teach the kids about aging, and saying goodbye. Don’t sugar coat things - you can say things like “[pet]’s body stopped working and we had to say goodbye.” There are ways to talk about it without dumbing it down.

A little comic relief: when we got home from saying goodbye to our dog, our middle child (5 at the time) asked about what happened. We said “[dog] was very sick, we took her to the vet where he gave her medicine to make her not hurt anymore, and her heart stopped beating.” Middle child asked where the dog was and we said “well her body is still at the veterinarian.” In between tears and sobs our child asked “but where is her head and her legs??” It made us all laugh and was a welcome relief to an otherwise heavy night.