Thanks to both of you for the insight. When we first got Lincoln, they approached him how you suggested. But I think as time went on, and he seemed to get used to them and be friendly with them/jumping and tail-wagging, things just sort of progressed, and then maybe went too far. Even sometimes when one of us wants to pick him up, he will resource growl.
Do a lot of puppies develop this tendency? I know you said all dogs are capable of it, but I feel like I "did damage" to his easy-going personality and the work to back out of it is going to be hard.
As Dave said, when he growls about being picked up, it's NOT resource growling. Resource growling is to keep some "resource" (food, a prized toy, a favorite sleeping space) away from another dog or person.
He IS telling you that he doesn't really WANT to be picked up right then. Certainly not ALL puppies (dogs really) develop this tendency, and some show their displeasure in other ways. Often, a dog who doesn't want to be picked up will roll over on his back, and give what is called a "whale eye" (showing the whites of the eye) rather than growl. This is often misinterpreted as either "submissive" behavior, or that the dog wants a belly rub. What he's REALLY saying is, "I really don't WANT to be picked up right now!"
How you handle it depends on on a lot of things. It should be respected, IMO, and unless there is a good REASON to pick the dog up right then, let him be. As I said before, they aren't toys, they are creatures with their own needs and feelings. And some dogs just NEVER like being picked up.
Very young puppies rarely object to being picked up. But if they are picked up to swiftly, or in a way that makes them feel insecure about falling, they may start to object. If you HAVE to pick him up, stroke his back gently (NOT his head... Most dogs actually HATE having their heads stroked... they just put up with it because they love us) then slide one hand under his rib cage, and the other under his rear end, so he is fully supported as you lift him.
Better yet, if you don't HAVE to lift him, find a way to get him where you want him to go without lifting. That might mean luring him with food initially, then later turning that into intermittent rewards for going where you want him to go.
A "for instance" is Kodi. (again)
Kodi relaxes on the bed with us in the evening, then goes to bed in his crate at lights out. He went through a period where he didn't WANT to get off the nice warm bed, where he was already asleep. (if it were only up to me, I'd let him sleep with us, but Dave has a "no dogs in bed" rule
) So he'd give this sort of grumbly growl when I picked him up to put him in his crate. He is very happy in his crate, so this wasn't that he had a problem with the crate... only that he didn't want to be moved. So we "sweetened the deal" by tossing a cookie in his crate and calling him to go to bed. His interest in food outweighed his desire not to wake up and move.
Now it has just become our evening ritual. At bed time, all three dogs are told to "go to bed", and the first one in their crate gets the first cookie. It's a fun game, and everyone is happy.
Interestingly, the two times he has stayed on the bed, not wanted to wake up and growled since we started this (years ago now) it turned out that he was ill. Once with an ear infection, once with a Rabies vaccine reaction. So if your dog growls at you in a way he's never done before, be alert to the fact that he might be in pain or not feel well. (though I don't think that's what's happening with Lincoln right now)
I don't think you've created a "big problem". But I do think you have to look at things from his point of view, and find a solution that works for both of you.