I planted four 2 foot tall paw paw trees yesterday (bought bare root).  The instructions that came with them say to plant directly into soil, no soil amendments, no fertilizer.
However, Most instructions I find on the net for juvenile paw paws say to fertilize them when planted.

All other instructions seem to agree though (keep well watered, protect from the sun)

I'm just wondering if there is any advice either way about fertilizing? 

I would use a root stimulant before I worried about adding fertilizer, pawpaw trees are very sensitive to sudden changes around their root system.

I like to wait till a tree shows signs of "taking" when I plant young trees, especially understory trees like the pawpaw, which does need shade the first two years of life.
These trees do best when planted in an understory where they will have to grow taller to find sunlight, that way they come into the light gradually and don't sunburn.

Redhawk

I actually already have about 8 paw paw trees that I have planted over the years. 

I grew those from seed, but I don't have any experience with bare root paw paw care. I'm just mainly worried that fertilizing them too soon might have a detrimental effect, though
like I mentioned,  the instructions that came with these particular trees said not to do so.

hau Cris, yep, I would go with their directions. 
I am impressed that you got pawpaw seeds to germinate, it can be rather tricky where I live (up on a mountain top and not down in the hollow where the stream is, which is their natural habitat).

The root stimulant is more of a root jump starter (I use old B-12 tablets dissolved in water). Once you see some new leaves coming out, you will know the tree roots are establishing themselves and will be ready for a bit of nutrient addition.