Got PS4 pro and a One X.
PS4 has been in its box a long time... if you play online for me the PS4 just isn't good enough. However if you play single player a lot, this is your console, the only time i will be pulling mine out the box anytime soon will be for Last Of Us 2.
For a child, the xbox is so child friendly and has a much better parent control. PS4's is virtually non existent. my 7 year old has a one S it notifys me when ever i buy something ( he knows not to anyway) via email for me to confirm it. If i dont, it doesnt go through.
Suppose it all depends what you child wants! They wont be fussed about anything other than the games they want to play, mines obsessed with roblox and minecraft, neither is a console decider, I prefer the safety of the Xbox parental side though.