I am by no means up to date on all the treatments available out there. There is a lot of research out there, you just have to kind of look around.
With children, I would think you would need to be careful of the types of "natural" remedies you administer as every child as well as adult reacts differently. Certain combinations might not be beneficial.
I also understand that for children especially there are a scope of "exercises" and games to improve focus.
I would say a combination of homeopathic, possibly chiropractic, counseling, good natural diet would be an approach. But you would want to consult with a professional no matter what.
There are many on this board who would be able to give you better specific information. Hopefully they will make a contribution soon.
Most doctors & psychiatrists will tell you that meds are the only way to go.
If a child has allergies or food intolerances, these can contribute to ADD, and can be dealt with w/out psych meds. Anxiety can contribute to ADD, and sometimes it can be helped w/counselling.
There are various vitamins & supplements that are promoted as being helpful for ADD. The basics: a good amt. of B vitamins, and Zinc. The other day I saw that Minute Maid OJ has one formulation w/extra Bs & zinc.
Fish oil has its following in the ADD natural remedy community; at age 7 yrs., you want one w/a fair bit of DHA, to promote brain development. Some EPA fraction fish oil is also a good idea, it helps with mellowness. You'd think it would be impossible to get kids to take FO every day, but Nordic Naturals brand has little strawberry-flavored (deodorized) gelcaps that can be chewed or swallowed. Kids love them! I have no affiliation w/the company. Often health food stores have samples available.
For bedtime/settling issues, magnesium is very mellowing. A handful or two of Epsom Salts in the bathtub in the evening can be relaxing.
Unfortunately, it can take a while to see an effect from nutritional approaches. They may be most helpful for the milder cases of ADD.
A 7 yo who is "out of control" may need more than just a few vitamins ... has your niece had an evaluation? Sometimes the problem is bigger than just ADD.
Neurofeedback is a nonmed way of improving attention & concentration. But typically a child needs to be able to sit in order to do it effectively.
Now I am not doctor nor do I claim to be, but I have a friend who's child has ADD as well as friends of her's who have children with ADD. One child was on riddlin and was a zomby at school. She recommended Chamomile pills for the hyperactivity. The woman who's son was out of control has absolutely no side effects and is showing no sign of his ADD. I'm not saying it's gone, but they believe that Chamomile pills are keeping him calm. I have even bought them for my daughter. When she starts her screaming fits I put 1 chamomile pill under her tongue (so it will desolve). It works wonders. Most of my church use it as well. I bought a bottle at a health food store for I think $14
There is much that can be done to help those with ADHD besides medication. Even if medication is used, it should be a small part of the treatment plan.
Your niece needs a well-balanced diet and a muliti-vitamin/mineral supplement is probably a good idea (because what kid eats a truly well-balanced diet?). Studies regarding the use of the Omega 6 oils - as found in salmon oils- have been somewhat promising. So, supplementation with a small dose of Omega 6's might be a good idea. Beyond that, the safety of heavy supplementation with isolated nutrients has not been proven.
*BUT* your brother needs to be looking outside of a pill bottle for a treatment plan. Family counseling is a good idea. Biofeedback has shown some promise. An IEP (Individual Education Plan) at school is needed. And, never under-estimate the importance of good parenting. Counseling can help there. Also, I can recommend the book "SOS! Help for Parents" by Lynn Clark, PhD. It was very helpful to me.