Without parents consent

I would ask to speak to the manager and inform them that your child was able to purchase this from their store without your permission and you want it returned. Although it is ok for kids to buy consoles since they don't have an ESRB or PEGI rating like
games and movies, I would still tell them at the store that your kiddo bought it without permission.

Hello, this is up to the retailers decision as the law varies State to state or country. If you say to them what happened they may refund you. If they do not you can take it higher with them and contact their head office as personally i think they should
not have sold it to him.

First you definitely do not want to give out your personal information in this public forums.

The only thing that would be restricted on purchases in regards to games would be the games themselves these have different ratings on them like Movies where the salespeople can not sell the games to someone under a certain age just like a movie theatre
can not sell tickets to a R rated movie to someone under the age of 17.

As far as returning the console that would be up to the store that he bought it from and their return policy.

I am sorry to hear that that happened. There is no age restriction on video game systems. To give an example my 6 year-old niece just went to gamestop and bought a Xbox One X. Her parents were outside the store waiting for her (it is a very small store)
the only thing she was asked was if she wanted the warranty on it. I would definitely reach out to the retailer he bought it at and see what their return policy is.

You can try to return but im not optomistic