Is there another forum here that might be able to answer my question about planting out tree seedlings?

I don't know if Trees, or Propagation forum would have anyone in your circumstance or not...

You have a couple of problems - I think by now you've figured out a clay pot isn't the best container for starting trees :) Your buckeye are most likely doing more underground growing than above the sowing medium where you can see progress - they have a taproot so depending on the depth of your clay pots, you've got issue #1. The second is more than one seedling/sapling in a pot - yes you will need to separate them. Or worst case scenario, choose the stronger specimen and cut off the second without disturbing the first.

Have the pots filled enough with roots that you can tip them upside down and shake the contents out? Catching it with spread fingers of course, not letting it fall to the ground.

Thanks for your input. I would have just started these seeds in the ground EXCEPT that I was out of state for several months and they germinated in the refrigerator. I understand that buckeyes are extremely prone to rotting because of high fat content so I did the best I could...what kind of pot (if you have to use a pot)would one normally start a tap-root type tree in? My clay pots are about 12+" high and yes, I can probably tip them upside down to get them out. What I was unsure of was how they would fare outside right now. The outside temp can dip into the 40's and I guess it's possible to still get a late freeze. Maybe I just need to get 'em out as quickly as possible? I have never had a place to plant in till now so I am fairly new to this :)

If they haven't been outside, you'll want to harden them off gradually (as much for wind as for sun) and it would be best to wait until after danger of frost. When you do plant them, will you be there and able to water through the hot months this first spring/summer season?

I get my supplies from Charleys, not that I expect every hobbyist to special order pots :) It can be difficult to find pots for plants that will form a tap root that are not as wide as tall and take up more than their share of room. My starter/first pots for indivdual trees, shrubs, perennials are 3.5x5" deep and I have a few of the tree pots, about 4x9" deep. You could get creative, use water bottles or litre pop bottles with drainage holes cut in (make sure they are adequate) and the tops cut off in a pinch.

Here is a link that might be useful: Charleys

Thanks so much for your help! I'll be gone for much of the summer BUT most of my property is woodland and in shade so I'm hoping that this will help. Just hope I can deer proof everything, though I *think* buckeyes are not a delicacy for deer. I did make a pot w/2 milk bottles for a paw paw once...guess I just didn't research buckeyes well enough...I will check out Charleys. Thank-you!