Planning to Barter/Trade/Sell my son’s stuff. Any suggestion?

My son will be turning two in four months time. As much as I want to be sentimental, I don’t have that much of a storage. I like the idea of paying it forward so I decided maybe it’s better to barter/trade my son’s stuff that he will no longer need or sell them for low price. Any other ideas from you guys? Or any suggestion where I can barter used kids stuff? Thanks!