I have a few suggestions, don't know how possible they are or not, but still:

First of all, I'm having a ton of issues making things intentionally hinge around an axis, for seesaws and that sort of thing. Is there any way to simplify this?

Secondly, this might be possible but I couldn't figure out how, a way to just start with an entirely blank slate, no ground, ball, or star would be nice, for when I just want to play around in a sandbox.

Third, the undo is useful, but if it would be possible to make an eraser instead, to choose which to get rid of.

Fourth, this is similar to the hinging thing I mentioned before, is it possible to make wheels that spin around a set axis?

Finally, this one is the one that is probably the most impossible of all my ideas, but I would love if there was a way to make a line a string instead of a stiff line. (This sort of ties in with the wheels because I was thinking for pulley type mechanisms, but probably too complicated.)

If it was possible to do the string idea, and expanding upon the whole crayon theme of the basis for this, it could be a different color. But instead of pressing a button to make that menu come up with the color options, maybe a skinny border around the entire screen made of crayons of different colors and to choose the one you'd like, just tap on it?

Like I said, some of them would probably be difficult or impossible, but just ideas.