A dog shouldn't really belong to any one member of the family. A dog is a member of the family in their own right.
No, you absolutely should NOT get a dog on the whim of a 5-year-old.
Dogs are a LOT of work, more work than you can possibly imagine when they are a puppy.
You will have to hoover every day.
A Golden Retriever needs a lot of exercise every day.
What about when you go away for the weekend?
What about when you go shopping and then it turns into lunch and then you want to go on somewhere but oh, you can't because the dog is at home?
Dogs smell and poo and are sick in the sitting room and take your lovely new scarf to bed with them and eat the loo roll.