My 4yr old son has a problem when he has a bowl movement its nearly always huge and takes hours to flush?

Constipated. Your child suffers from chronic constipation.You need to be aggressive with management.He has to go daily , about 2 to 3 times per day.You can give him MiraLAX (polyethylene glycol) or pedialax .They are available over the counter.Modify diet and drink plenty of liqjuids.Please see your pediatrician.You do not want child to suffer from fecal soiling nor get UTI urine infection!
Huge means retention. Kids of any age can have slow "transit" or decide to forgo a stool when the feeling arises.If a kid creates 5oz/day & empties only 4 or skips, the end of the colon can baloon out become less effective when empting occurs. What u describe is common. I have the radiologists clean out about 1/yr with a special enema from the 2 dozen i rx /yr when agressive home care doesn't help. Talk with your ped.
And... If you are asking if it is a problem only if your child has negative symptoms, such as abdominal pain, extra gas, blood in the bm, or urinary problems. If he is acting normally, I do not think anything needs done.