When jack and Jill fetch the the pail of water what kind of energy was that?

Jack and Jill went up the hill to fetch a pail of water.

In this case, they are converting chemical energy (their food) into kinetic energy (to walk). As they rise, kinetic energy is converted to thermal energy (part of the walking- they get hotter) and to potential energy (they get higher).

Jack fell down...

His potential energy was abruptly converted into downward kinetic energy, causing him (and later, Jill) to move down the hill.