I can't even count time number of times I got a gift from my mom or grandma, I wear it, they compliment me and I say, thanks, you gave it to me. There response- I did??? Lol.
Imagine one of those gift-givers saying, "I want you to keep this forever. I don't care if you don't have any use for it. I don't care if you don't have room for it. I don't care if it makes you unhappy because you can't manage the house. I don't care if your son is unhappy because you are unhappy. The most important thing is not your happiness or his happiness; the most important thing is that you keep and cherish this thing from me."
Can you really imagine them saying that? If they did say it, wouldn't you say, "Yikes! In that case, please take it back now!"
It's common to have trouble getting rid of stuff, and gifts are one of the categories that are hard to get rid of. But I think that it's best to think of that as being rather like a phobia or a bad habit--something where you understand that your thoughts are illogical, and you work to change those illogical thoughts.
If a thing isn't serving you now, and you don't have *very* strong evidence that it will serve you in the very near future, odds are that that thing should leave the house, gift or no gift.
This "stuff" issue just gets a LOT worse. Every birthday, Christmas, get-together, can become a chance for your son and future children to get a new thing-ma-jigger. Thankfully, at this baby-stage, your son has no attachment to these items. You should be ruthless about keeping only what you want and need.
I find it difficult to get rid of toys and junk (misc. trinkets, papers, etc) these days because the kids notice and are unwilling to part with them. We have dozens and dozens of stuffed animals! I just keep thinking, "this too shall pass!" With three kids and ten years of events behind us, it is a challenge to stem the flow! I am reading "Parenting Without Borders" right now, and really inspired that giving our children MUCH less is really the very best thing for them. One of our recent successes was my daughter's 6-year birthday party. We just invited four other girls, and received small gifts from the three families of the girls - a book, two small horse figures, and a craft project. Grandparents brought some gear she needed and an American Girl Doll. To me, it was a huge success because she enjoyed the party, but it wasn't overwhelming to any of us, and the inflow of stuff was pretty tame.
Best of luck as you start navigating!! This is a hard thing for us Americans!