one side to be very narrow. Put the lead in and heat it on the stove. I then pour it out the side I narrowed.
Been doing this for many years as a dad and with my dad when I was a cub.
I will note that it isn't safe for a kid to do on their own. You should use pot holders on your hand and clamp some vise grips on the un-crimped side to help with the pouring.