Hi :)

First up, the obligatory "I'm new here, I'm not sure if these types of posts are allowed" disclaimer.

I wanted to start a bit of an indoor vegetable garden, so I stole/borrowed some compost that had been sitting at my parents house unused for years. It worked incredibly well and my tomato plants are turning out awesome. However, there must have been something already in that compost because all of this started growing:

https://imgur.com/a/etLh3bj

My dad put in the general category of "weeds" but I've kept it anyway because, honestly, having never had any kind of plant life grow in my home before, I think it looks really cool and interesting.

Anyway, I can't seem to figure out the actual name of it and I wondered if anyone had any ideas. Also, if it is "just weeds" is there any harm in keeping it?

I've separated it from my tomatoes and other vegetables but it's growing so fast I'm not sure if it's going to become a pest or anything.

TL;DR: Totally beginner at indoor gardening. These plants started growing. Need help identifying them.