When children are urinating frequently as you describe, it's a good idea to have a urine test to rule out urinary tract infection or diabetes. Usually, though, if there are no other signs of these disorders (fever, stomach or back pain, burning or pain with urination, tiredness, increased appetite and drinking) then it is not one of these.
There is a condition that is very common, called benign urinary frequency of childhood. It's a condition that leads to very frequent urination, often as much as every 10 minutes. It's due to the bladder contracting frequently, giving the urge to pee. Usually these children pee very little each time. It will go away on it's own, sometimes in a few days, sometimes after a week or two. I usually recommend to parents that they put their child on a voiding schedule - they get to pee every hour, and if they ask in between then you distract them with other things. Then you stretch it to every 2 hours and so on.
I hope this was helpful.