I have bought a large bundle of second hand clothes for my son at each age group to be the bulk of his wardrobe. It means he has many many everyday clothes so I don't have to stress about washing, it's also much cheaper and better for the environment (I hate the idea of something being worn for just a few months then discarded).
We don't need to do this, could afford new but choose to buy second hand due to the environmental reasons more than anything else. A couple of people (friends and family) have mentioned that they find this odd, not really provided any reason why, other than we could afford not to. I do buy him new bits and bobs if I particularly like them or he needs something for a special occasion.
I would (and occasionally do) buy second hand for myself, but tend to have more new things, but do wear them til they wear out completely, so IMO not as wasteful as buying new and discarding after a few months as you have to with a child due to growth.
When he is older and growing more slowly, so getting more use out of things, of course we'll buy more new.
I think second hand is fine for now, AIBU?