I had several MA practitioners and MA newbie parents asked me how I kept my son interested in Martial Arts. The truth is I really don't know the answer but me and my wife gave lots of support when he was just starting MA. He often got injured during Judo and lost many competition and he personally knew and admitted that he sucks during compes but this never discouraged him. We were always there to watch their compe and mom said that she knew that me watching the compe gave my son more mental pressure than his opponents, lol.
Though you may see in our training vids that I'm often jolly during training, I have a different attitude during compes probably because that I came from a no holds barred offensive art, that losing in a closed door compe is not an option especially when my teachers have their bet on me. I lose = I get blamed and get my ass kicked by my seniors but if I win, I share the loot. It was not easy to have funky MA teachers who were expecting the loot so that they can use it as capital for roosters (cock fighting), lol.
Going back to the topic... The idea or advice on how to keep my kid interested in MA came from my seniors from Motorcycle Trials. During those days I was more on bikes and totally forgot about MA. My seniors shared with me their mistakes why their kids didn't follow their hobby. They said that when their kids were young, they really pushed them to ride BTR (bike trials) or Trials motorcycles and train like pros. Lots of technical stuffs, lots of balancing act and endless practice. Crashing is a common thing in Trials and some of the newbie kids freaked out and hated riding. I also got my son to ride motorcycles during his early years but kept my seniors advice in my mind and tried my best not to be too technical and just let him ride without pressure. I brought him to the mountains riding bicycles, scooters, , dirtbikes, Trials, ATVs and even normal streetbikes just for the experience and he loved it. I also taught him how to restore/repair and even help me salvage/scrap crappy motorcycles since he was 9 and he enjoyed it. Even up to now he still keep his crappy 250cc Trials bike though I rarely take him for riding.
Same with his MA training, I encouraged him to learn different arts and find what is best for him. I know that Traditional FMA was a bit hard for kids since he has to learn and experience lots of weird stuffs outside FMA like learning how to ride motorcycles, drive cars, repair vehicles, play with electronics, learn how to open locks, weld, hunt, cook, swim like a fish, climb high places, lots of survival training, etc. Plus I also encouraged him to watch the news (weird stuffs), lots of brutal/gore movies, lots of action and military movies, lots of games that are not intended for kids but we talk after and asked him his opinion if what he saw was right or wrong then told him the consequences if he unlawfully use what he saw or learned. Learning right and wrong is very important especially for Traditional FMA and CQC since these are very offensive arts. We practice with weapons but most of all our art is more on silent sentry style and in the wrong hands of a crazy skilled practitioner, this can cause extreme havoc which I strongly detest. Knowing that my son knows "right and wrong" and knows that he will go to jail or get killed if he use the arts unlawfully, I can say that he can safely learn other MA without being too confident, high pride, being a bully or acting like a thug.
One problem with new black belts or new advance practitioners is that often the advance newbies have too much confident and believe that they are somewhat like Superman or are knifeproof/bulletproof and can't be hurt but with how I trained my son, he knows that there will always be someone better than him.
Often when there is a new student who was awarded advance level, we (senseis) often talk to each other that we now have to break the student's pride so that he will not go astray. Breaking their false pride will make the newbie advance fighter to study more and to train more harder. They will become more open minded, more sensitive and more caring and if ever they may encounter real combat, they have a choice whether to use full force, slight force or just to run away. Most of the advance practitioners I know will say no to a fight and will only fight if there is no choice left.
It is really hard for us parents to get our kids constantly interested in MA. Most of the young practitioners will stop when they reach advance or black belt and many will not even reach advance. Being a parent of a MA practitioner can be hard to some, years of training/studying fees, lots of MA tools like protectors, gis, training wear, lots of laundry, driving them to the dojo or practice area, watching our kids get injured, losing in a compe, talking with other parents which we don't get along well or by just waking up early on a cold Sunday when we still like to sleep but have to rise and prepare our kids for their practice. Kids don't usually see our efforts but we really can't complain. All we can do is to guide them and hope that they will win even 3rd place in one compe...
I think the best way that we can keep our kids interested in MA is to regularly talk with them. Listen to their stories on how they trained, how they sparred, learn their dreams and goals, but most of all is to learn if they had fun. If kids don't have fun, they'll surely be quitting very soon... One style I use to get my son more interested in MA is to ask him to show or teach me the techniques he learned. Sometime I also study their katas or forms (from other martial arts) and practice with him. Often I ask my son to use the techniques against me and fake the act making him believe that his punch felt like that I was hit by a bulldozer but those were during his younger years now I have to dodge or ask him to keep his hits lighter or I'll be in big trouble, HAHAHA! In total, we try to make every practice or training as fun as possible so we both enjoy it. There is always a huge burst of laughter every time we do our training and when this happens, mom usually joins in. Often times mom will attack without warning and get our asses kicked. Probably mom is our secret weapon, lol.
Hope that you too enjoy training with your kids :)