Congrats on your new fuzzy friend.
let your hamster settle more. Id say 1 more week if Oreo seems to be on the more relaxed friendly side, if he seems more nippy id say 2 to 3 more weeks.
During those weeks, change his water when hes awake, clean his wheel when hes awake, and give him food in his bowl or scatter it around. This will let him know that theres other people around and that they arent going to harm him, it'll let him get used to the fact sometimes hands are going to be in his cage and around.
After that i would try to get him to take food from just ur fingers, have your son do this too at times and make him aware to be gentle, still, and kind with Oreo. When oreo is comfortable with this, you and your son can start putting treats in the palm of your hand and seeing if oreo comes up to you guys and takes the treats. Once again, when everyone is comfortable and used to this, you guys can try the bathtub. let oreo roam all over you and your son in the bathtub and try to pick him up by scooping him up from the bottom. good luck with your friend!
If you need any more guidance or visuals, you can try looking up taming methods on youtube, i recommend watching the channels ErinsAnimals and Victoria Rachel for those videos and general hamster care.