There are many possible wildflowers these seedlings could be (any monocot like plants in the Lily, Asparagus, or Allium (onion) family).  Solomon's seal would be in the Asparagus family, but usually their leaves would be wider even as seedlings.  I think you'll have to wait until one flowers to be able to tell what it is unfortunately, or you can try to find someone who is familiar with the flowers in that particular park.  Looking at iNaturalist (https://www.inaturalist.org/) it could be Cardamine nuttallii, small camas, white brodieae, ookow, or a few other plants.

You might look at the plants listed here:
https://www.chickadeegardens.com/2017/04/native-wildflowers-of-mccormick-park.html

Sorry I can't be of more immediate help.