Charlie is in remission, fully cleared medically, and finally getting back to being a normal kid, right? And Danny gets more time with he and Grace, and when Rachel tries to argue she realizes that she doesn’t have a leg to stand on.
Charlie is in a cars/trucks/boats/planes/anything cool with wheels phase and Steve is obviously the cool uncle because he lived on a ship for years and he knows all these cool (and child appropriate, thank you very much, Steven) facts and tidbits about life in the Navy and he’s got stories out the wazoo from his deployments and Charlie is in awe.
So, as a surprise celebration, Steve takes him, Grace, and Danny to tour the USS Missouri one weekend because he knows the tour guide. Charlie is enraptured by both the ship and WWII vet Ed McKay, who spends the entire tour grinning and ribbing Steve because this time he brought “the wife and kids” with him. And nobody even got shot this time.