Trix are implied to only be for child consumption, however that is not the case, as i am sure that many adults start off their day with a heaping helping of trix, and children cannot prepare their own trix and therefore they cannot "make" their own trix
Although many adults eat Trix, you can ask anyone and they will tell you that the target demographic for Trix is children. If it weren't then the mascot wouldn't be a funny human-sized rabbit, and the slogan wouldn't be "Silly rabbit, Trix are for kids!" This slogan says it all, and all the adults who eat them are outliers. Most children can prepare their own Trix, and if they don't, then they're not old enough to buy it either.