How to tell kids we're putting dog down

Boymama • Just had our third and last baby! #boymomforlife 💙💙💙
So our 8.5 year old dog is very ill and getting worse. Our kids (6 years and 3 years) know she not well but don't know the extent of it. Should we tell them before we go to the vet and let them say goodbye or should we wait and tell them she passed in her sleep? 
DH and I disagree...

Vote below to see results!