Is it okay for Catholics to use yoga as part of an exercise program? What about in physical education for children?
Two factors are relevant here: First, it depends on whether the yoga is being presented in a manner that is free of religious elements, i.e., purely as a system of physical exercise. If it is coupled with elements of Hindu spirituality (e.g., talk about moving kundalini, or energy, around your body), it is not appropriate for Catholics to use it as part of their exercise routine.
Children are not mature in their thinking, and while an adult who is firm in his faith might be able to go to an “iffy” yoga exercise class without danger of being attracted to Hindu spirituality, a child well might not. If a child is being put in danger of being attracted to Hindu spirituality–either now or in the future–by the program, then it is not appropriate.