the third one is a poppy

No.1 maybe Pokeweed/Pokeberry
No.3 poppy

Just woke up....so no idea on the other ones just yet, but I'm thinking LOL!

The third looks like a poppy.
The fourth looks like a peony.
I don't think the second one is a weed, but I don't know what kind of plant it is.

Wendy

Fourth looks like my peony.

hmmm i've seen the second one, i've planted it, don't remember the name, LOL the last one is a fly!! yep, i'm pretty sure,!! LOL yep it does look like my peony's when they first come up. SORTA LOL but not that skinny of leaves. i agree with the poppy. we got them growing in talla's fairy garden!! :'))
or maybe the second could maybe be a buttercup?? it "kinda" looks like that. hers are bigger now, but i think they looked like that as seedlings. Medo

My regular Peony leaves are much different than those. That looks like a tree sapling of some kind.
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Oh no Vera! No offense but I hope you're wrong about the first one being pokeberry. I don't need any of that. I need to post another photo of that seedling to show the pointy leaves better. I think the tips on pokeberry leaves are a little more rounded and I don't think the leaves have a reddish edge like that. Do they? Sigh...It wouldn't be the first time I've nursed a weed.

The 4th one looks something like my WS Cosmos 'Bright Lights'. Here's a pic I took yesterday -

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I would say the third one is a poppy. I had some that look almost identical to those pop up that I never planted ... must have been bird sown. Others on the forum thought them to be Shirley poppies.

Number four looks a bit like my cleome seedling.

Terrene - Your cosmos does seem to be a match for the fourth picture and I'm sure I had cosmos seeds. I have some other seedlings with feathery foliage that I'm sure are cosmos but a different type.

I googled some photos of poppy seedlings and they do look like the third photo. I don't remember having poppy seeds but may have.

The first one is still a mystery. I compared it to the poke growing in my yard and they look a little different to me. Any guesses?
The second photo is still a mystery too. I don't think I had buttercup seeds. I knew I would regret not making a list of what I planted but I had so many different old seeds and was in a cleaning frenzy. It's only about an inch tall right now so I can try posting another photo when it gets bigger.

Cosmos bipinnatus has the feathery foliage - and the varieties I have grow very tall. Cosmos 'Bright Lights' is a cultivar of Cosmos sulfureus, which apparently doesn't have feathery foliage (my first year growing these).

The first seedling is definitely not Pokeweed. I've got zillions of them around the yard, and am constantly weeding them out of the garden. Their leaves are greener, larger, and rounder on the edges.

Could the first one be some kind of Amaranthus?
I sowed some Love Lies Bleeding and when they were younger they had the same red stems and reddish tint to the leaves:
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The leaf shape is different though...

I googled pics of Pokeweed and yes, it looks like some of them do get a reddish margin on the leaves and stems at certain points of maturity. Try Google images.
You know now I have to agree with the guess of Cosmo sulphureus on the 4th too LOL! Here's foliage of Cosmic Orange Cosmo last year in July and a seedling pic of this year:
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That's interesting the foliage is so different on different types of cosmos. I'm guessing seashell cosmos are Cosmos Bipinnatus, since the foliage on my seedlings are really feathery and don't look anything like the above photos.

Cosmos seashells is Cosmos bipinnatus. I've got reseeders of several varieties of C. bipinnatus in the garden and they are so beautiful but they get really tall, even with pinching. I usually have to stake them a little or they lean over. Worth it though, the pollinators and birds love them!

I'm hoping the Bright Lights doesn't get so tall.

They key with C. bipinnatus is too not feed, full sun and not too fertile soil. They'll stand proud :)

Vera

Follow-Up - Could the first one be celosia? It's starting to get a little fuzzy thing at the top. : )

Guess it could be. I'm doing celosia for the first time this year, but still little tiny things. They are in the Amaranthaceae family, so the mention of Amaranthus above may just have been right on with the similar looking leaves :)

My Celosia germination sucked btw....I planted out like 3 babies from 4 different containers.

Vera

If it's celosia, they would be from seeds that were about three years old that didn't germinate for me when I tried to winter sow them the first time. They must've have better conditions this time because I have a bunch. Isn't that weird.

I can't find the second one now. It either croaked after being transplanted or I've forgotten where I planted it and I'm looking in the wrong area. : (

second one could be aconitum, anemone or cimicifuga- actea. Now that is gone I guess it does not matter ;(
first one is amaranth and third is poppy