Unknown plants grow in my pots
I used the 2 pots to grow tomatoes, but they all dead before they flowered. I left the pots by the window(it was closed most of the time). After a couple of weeks, I found some small leaves on the pots and they were kind of even arrayed. I really want to know what am I growing?
I'm sorry your tomato plants didn't pull through! It's difficult to tell what could be still growing in your pots without seeing a photo. I doubt it's new tomato plants (but wouldn't that be cool?).
I sometimes mix dirt or compost from my yard with potting soil which results in the occasional weed growing in my pots, so that's one possibility if you did the same thing.
If you don't mind the pots sitting on your window for a bit longer, consider it a fun experiment while you wait and see what emerges!