Vitafusion makes a peach-flavored gummy version of CoQ10. I've seen it sold at Target stores in the US; I don't know its availability elsewhere. The 6 mg deflazacort pill is very small. My son (almost 6) swallows it with a bite of pudding or other soft food.
Coenzyme Q10 is an antioxidant. Oxidation (= chemical reactions with oxygen) is a naturally occurring kind of damage to molecules, and it can happen to molecules inside cells, and that can help lead to health problems, which is why antioxidants are a hot topic. (If your cells don't work right, your body won't work right.)
Antioxidants are used to bind up loose oxygen in order to make the oxygen less available to react with other molecules. Oxidation has a role in DMD (it's one of several things happening to cause damage to the muscle cells). I don't know how much evidence there is yet of measuable results in DMD, but it's one those things where you figure: it's cheap, it's easy, and it doesn't cause any harm. So a lot of people use it, both for DMD & for general health.
CoQ10 is marketed for heart health, but I suspect whatever benefits it has aren't limited to the heart. It won't give more strength. It may help slow down damage.
Liquid from EOIC is very good. My sons levels went up after using it. I changed to the chewable this time and while my sons takes them, he does not like the taste on the chewable. I will switch back to liquid next time.