It is difficult enough to select the "best" curve. So scatter the curves face up and take a close look anyway you like - but don't "try out" curves by placing them into the playing area and putting them back in the supply if the result does not please you - if you want to play in the spirit of the game.
A watertight rule would be: scatter the curves face up at the edge of the playing area so that no curve touches the other. When it is your turn to take a curve take a close look and select one - use two fingers to take it at the end that you intend to touch your "book" (thus you decide the direction in which the curve will run later when placed in the playing area).
Hope this suits everyone :-)
Oh, and I would propose a slight variation: If children play - allow them to do what they like - after all, it's a game ;-)