My two year old nephew had issues with balance and falling over due to an inner ear infection.
It is best to have him assessed by a doctor. It always pays to err on the side of caution, especially with young children.
I recently watched this show about feet. I was particularly interested because I had super flat feet when I was a kid and fell often enough (scars on knee to prove it). Not that I'm saying you shouldn't go to the doctor (by all means). Just something to keep in mind.
Childrens feet aren't fully developed. Correcting a "problem" now could result in the foot not develpoing correctly on it's own. Look it up, I think it may have been a PBS special.
As an adult, my feet are fine (much less flat) and even stubbing a toe doesn't result in a fall. In fact, I haven't fallen in years. Glad my parents didn't have the resources to "fix it." Especially after watching that show.
Welcome to the MedHelp forum!
If a child who is 5 years old falls a lot, he could be having foot anomalies like flat foot or a pronated foot or even a knee deformity like locked knees. Get this checked out by an orthopedic specialist. Endocrine deficiencies, low blood pressure, nutritional deficiencies, problems in the cerebellum portion of the brain, wax in ear, ear infection etc all can be the cause. It is important that you get your child evaluated for this. Please consult his pediatrician. I sincerely hope you are able to find an answer soon. Please let me know if there is any thing else and do keep me posted. Take care!