Unfortunately we are unable to recommend Ginkgo Biloba for children as the safety evidence is inconclusive. 

In terms of ADHD, the effect of ginkgo on symptoms related to ADHD is unclear. There is early evidence that a product containing ginkgo leaf extract and American ginseng might help improve ADHD symptoms such as anxiety, hyperactivity, and impulsiveness in children 3-17 years-old. But other research shows that taking ginkgo extract does not improve ADHD symptoms compared to methylphenidate, a drug used to treat ADHD, in children 6-14 years-old. Also, taking gingko extract along with methylphenidate does not seem to greatly improve parent or teacher reported ADHD symptoms compared to methylphenidate alone in children 6-12 years-old. 

We would advise that if you proceed, you do so with care.  More information on dosage used in the trail can be found at https://www.ncbi.nlm.nih.gov/pubmed/25925875 . Please be aware there are numerous interactions between medication and gingko biloba.  

We would advise consulting your child's GP or consultant before taking food supplements.