Thanks everyone for your replies, Jo please don't feel you've 'hijacked' my thread lol I hope you get the help you're looking for too
Charlie has a dried complete puppy food which was recommended by our vet, its a local pet suppliers own brand. He has 1 cup twice a day which was equal to the recommended weight on the bag, I've just used the last of the food and have thrown the bag out so I can't remember the exact weight. Jazz is on the same food and she wolfs it down and is fattening up nicely but she's only 14 weeks old. They don't have many treats, only training treats whilst out walking and maybe a pigs ear once or twice a month (I've also just read on here that these aren't good really so I don't think we will be giving them again - shame really they do love their pigs ear, and it keeps them quiet for ages) lol
I think maybe it might be time to try Charlie on adult food and see how he goes. He was weighed at the vets when he was last wormed(about 6 weeks ago) and he was 13.8kg does that sound about normal? He is VERY energetic, I'm presuming this is why he's so slender.
Thanks again guys