I have a small area in my backyard where I have put in native grasses
(indian grass, switchgrass, little bluestem & big bluestem) It is
coming up slowly, I planted from seed about 8 weeks ago. Now the
tallest seedlings are about 3/4 to 1 inch tall.

Problem is there are a number of weeds in the area. Do I pull them,
or just leave them and assume the grasses will eventually grow over
them and make them go away?

It is a 20 foot by 10 foot area that I had always just let my regular
grass grow long, the kids love to catch insects in the area, so I
finally bought to some native grass seed, it should be cool once it
gets tall..