Help with American Pawpaw seedlings

Way back last November or so I put 6 pawpaw seeds into a pot and left it outside all winter, despite having no winter to speak of a rummage around in it in May showed that all 6 seeds had started to germinate. Now in mid august three of them have finally decided to throw up actual leaves. (we had a very cold July coldest in 150 years!) How big do these things need to get before they have a chance to survive winter? and are they likely to manage that in the month and a half we have before first frost? They are sitting on the north side of my house at the moment so mainly in shade all day, but they get a tiny bit of sun very early in the morning.

They will probably be fine if you put them in the ground now. The continental U. S. gets colder winters than Denmark, so the seedlings expect a freeze.

They develop a really deep tap root in my experience.  I would put them individually into really deep pots if I was going to try and winter them in a green house out indoors.

Best bet is to split your group half in 12 to 18 inch deep pots and half in the ground. They are understory trees here and mine have done well even as tiny plants in winter  as long as they are dormant before frost and also providing that you mulch them deeply as they would experience from leaf litter here in Appalachia.
I have not got a great deal of experience but i have raised 3 from seed over the past 3 years. I usually plant things with compost and deep mulch and then give them lots of neglect. It seemed to work especially well for my papaws 3 out of my 4 seeds are now shoulder height.

I have read that they prefer more shade until their 3rd year and then they really hit a growth spurt and enjoy lots of sunshine. Perhaps if you plant them in a sunny location you can put a tomato cage around them with shade cloth it will cut down on winds and intense sun and can be easily removed later.

Best of luck!

3rd year from seed this is a picture from earlier this summer. Ill get another when I go put up the ducks