well i would'nt think so as he's getting some of his 5 a day,but i reckon the proffessionals would say it would be better to have a varied range of fruit/veg rather then 5 of the same,but if i were you id go and check with the gp just to make sure!
I should check this out with your practice nurse. It may be fine, but bananas contain a high amount of potassium - which might be beneficial if you're a stressed-out adult - but may not be so good for a 3 year old.
Thanks, everyone. I had wondered about the amount of potassium per ratio to his little body but could find nothing on the internet about any harmful side effects or what a safe intake should be for a child.