I'm thinking of using this program from about age four when I have children, in order to build a good grappling foundation, and perhaps enroll the kid into a children's judo class later on. As the Bully Proof program is essentially Gracie Combatives minus the choking techniques (which is VERY understandable), I believe that the focus on base, positional control and basic submissions, all of which are allowed in Judo(since the chokes isn't included), will be a great base and provide a good advantage in Judo ne-waza when he/she starts doing Judo. The Bully Proof/combatives takedowns would probably not be that usefull, considering that morote gari were made illegal in competition in 2009 I believe, and the rest of the takedowns, including the ko soto gari variant they teach, is based on attaining a type clinch which would be extremely hard to get in a Judo setting.
I'm not going to teach my kid any Hapkido until far later btw.(if they are still interested), as the nature of many of our techniques, just as with the chokes of BJJ/Judo, are disasters waiting to happen if used irresponsibly in the schoolyard. Judo/BJJ is super effective in itself, and in either case, I generally don't want my kid to be able to do anything worse submission wise than popping an elbow, until mature enough to handle more destructive techniques.