How much space is between the individual seedlings popping up? How many rows do you have 4" apart? You probably won't be able to transplant any to a new spot, since these are all root plants. You can eat the beet thinnings - just throw anything small into a salad. Radishes can grow close together, so I might not worry about those, just harvest some of them small to give others space to keep growing. With carrots, make sure there is enough room between seedlings for a mature carrot's "shoulders" - so depending on variety - an inch or so. With those, I would just snip those that are in the way with scissors. You don't want to rip up neighboring seedlings by pulling them up by the roots.
What you do get will be yummy!! have fun!