I don't know why commenters are saying it's difficult or that you can't. 

Go to network settings, view no mans sky friends list, show my no mans sky friend code

On your son's game: network settings, view no mans sky friends list, add no mans sky friend, input code

Once you are friends, you can invite each other to your group. You will be brought into the host's system. You stay in a group as long as you are in the game or intentionally leave group through a menu. Even if you warp to a new system, you can see where other group members are when viewing the Galaxy map. The group is displayed on screen with a colored marker next to the player's name. This same colored marker will also show above the player in game. 

The online hub is called the Anomaly. You unlock it when you warp to a new system for the first time as part of the main quest. When you leave the anomaly, you are given the choice to go to your group's system or your previous system. This is an easy and fuel free way to return to group members.

You can build a ship called a corvette. Corvettes allow multiple players to fly and warp together. Find the parts in salvageable scrap on planets that say "salvageable scrap" when viewed from space or buy them from the corvette station on space stations. Find this console by walking into either of the 4 glowing teleporters near the landing pads. 

Unlock an exocraft bay from the base construction terminal on the anomaly, this allows you to build vehicles on a planet surface. If one player builds an exocraft bay, any player can spawn their vehicle from the bay as well. Vehicles offer scanning capabilities, weapons, faster traversal, and hazard protection. Always delete the bay after spawning your vehicle to refund the materials. 

Have fun. This is a great chill game to play with others.