The thing is, we are alive for a few decades only. After your death, there will be no museum of your child (at least, it's a very unlikely scenario) and the only person who wants these things, on some level, is you.
Therefore you'll either keep things until you die and someone else will chuck them out, or your child will reach adulthood and you'll try to give them these things and believe me they will NOT want them, and they will chuck them out.
If you keep them, they will just use up space and make you feel all weirdly emotional and possessive and you'll kind of resent them being there but be unable to get rid. What a mess.
Just keep the things you are likely to re-use for your next child, donate or recycle anything you won't reuse. Pick out a small handful of sentimental things if you like, and hang on to them. Preferably things that are small, and can be displayed or kept somewhere like a memory box for you to look at from time to time. Take pictures of it all if you want, so you still have something to look at after it's gone.
My mum was a bit like this over baby stuff after younger sibling grew up, holding on to all sorts, even down to toiletries and things that shouldn't be kept for very long. I think she could have done with some counselling tbh, as it's usually not about the stuff but about the emotional attachment to things stemming from childhood events like bereavements etc. It makes me sad to think about it really.
Stuff is just stuff OP.