B.A.
Before trying this or any product that is saying it is safe for kids. And you may already have, try other avenues for help with concentration or ADHD type symptoms. Please take this as a suggestion and not a criticism as only you can do what you feel is right for your child and family.
Make sure a child who seems unable to hold focus has enough physical exercise daily, outside time minimum 1 to 2 hours outside, it's okay if it's above 10 below 95 and not thunder and lightening and not any other dangerous conditions. Enroll them in a sport(work on finding the one they if not love, can tolerate) and if possible even young expose them to music either learning an instrument or dance.
If homework is an issue have them sit on a flexball while doing homework and if this works at home it may need to be carried in some way to the classroom.
Good solid diet, get rid of food dyes as much as possible. Have the child tested for allergies and intolerances such as diabetes, celiac, thyroid, nuts, peanuts, soy, shell fish, etc as some of these will "block" the ability to focus.
I would try these routes before investing in a "product" of any sort, including medicating my child by prescription...you will have to work to find your childs route to learning and calm.