touch 0 end - create objects on [square.X + random(-square.width/2, square.width/2), square.Y + random(-square.height/2, square.height/2)];
it's an approach of a square.
If I remember my last solution for it, I'll come here and share.
Edited:
If your radius is the same circle width/2, use:
= Touch 0 end
-> Create objects on [circle.X + cos(random(360) * circle.width/2), circle.Y + sin(random(360) * circle.width/2)];