Fruit is very good for them and it is a great help on bowel movements. As long as they are eating other necessary foods then let them have all the fruit they want.
Although my DS eats lots of fruit I do have to watch it, too much leads to diarrhoea and left entirely to his own devices he would have eat too much fruit and not enough from the other food groups. I believe in self regulating but I also believe we need to offer the right balance of foods too.
Tink sounds like your LO has a big appetite
Some times mine amazes me, I have to design his day to get protein into him as he is not a protein fan, then suddenly he eats almost an entire lamb shank in one sitting!! Seriously there was about 2 bites and the bones left. We all watched in utter amazement.