Mine lived in onesies and rompers.

I put my babies in lots of rompers for the summer. And in a long-sleeved onesie and sleep sack at night because of the air conditioning. Long sleeves and pants will be too warm for being outside in DC. I put a blanket over the baby and socks on their feet for things like doctors visits where we were inside for a short time. You are probably seeing lots of long sleeved things because of the time of year. In March, you'll start seeing more summer stuff at the store.

Carter's, Target. Many summer babies just wear a onesie (no pants). I personally liked putting my kiddos in short-sleeved rompers - they are easy as onesies but they look a little more like a whole outfit bc the legs are shorts. Like this: https://www.target.com/p/baby-boys-tiger-striped-romper-just-one-you-made-by-carter-s-orange/-/A-82004297?preselect=81812902#lnk=sametab

Like others said, I wouldn't load up on stuff yet. It's hard to know when babies will hit each clothing stage - you could buy a bunch of newborn onesies and have a baby who wears 0-3m from the get-go.

Thank you for all the advice! I'm due in May, so just heading into the summer. We let our house stay pretty warm in the summer (76) and like to go for a lot of walks in the summer evenings.

You need both—assuming your home is air conditioned and kept cool.

Agree not to buy too much in advance. In your case, I'd focus on the 3-6 mo size. Many kids never wear newborn sizes at all because they are born too big, and even if they do it's for like a minute.

Then you'll need some 0-3 month stuff but I'd just do the bare minimum for two reasons. The first is that they will likely outgrow it before they hit 3 months (I had a 50th percentile baby and she did). The other is that if you have a child under 3 months in the summer in DC, they will wind up being mostly naked a lot of the time. Mine slept in nothing but a diaper and a swaddle for the first two months of life (July baby) because anything else left her sweating. When we went out, she generally wore a short sleeve onesie and some socks (which she instantly took off). I'd bring a pair of loose cotton pants (in a 3-6 month size, I don't think I even had pants smaller than that because newborns don't need fitted pants) and a cotton cardigan in case we went inside somewhere with air conditioning. And that's it. Even outside the house, she spent probably 70% of her time at that age in a carrier, and I dressed us both lightly so that wouldn't be too uncomfortable.

For brands, Carters is great for onesies. I also relied on Target a lot at that age. Their Cat & Jack line is great for babies and toddlers -- very soft and stretchy and come in cute prints. Also really affordably priced. I also always kept my eyes peeled on my neighborhood list serve for people getting rid of baby clothes -- you can get a whole bag of hand me downs that way and it's like a little ready made wardrobe for the next couple months before your kid grows and needs more.