As an animator myself (though not stop motion), just encouragement is probably best. Some decent software will help. Top of the line is Dragonframe though there are plenty of others out there. Something that has camera control and onion skinning is best. Also learning traditional animation (ie stick man) will help him get timings and movements bette. There are so many parts of the art, it's just a case of practice, patience and being totally aware and observant of movement.