I had a friend had a cat called Square, because he was. He used to feed him on top of the fridge; when he got too fat to jump up there, he got not food and lost weight until he could jump up again!
Polly sounds plenty active enough but even so I would do the usual things to keep an eye on her weight. Just like dogs, you should be able to feel but not see the ribs - if you have to press hard to find them, she's fat!
As a guide, I have always fed my adult cats (all of whom have been very active hunters - and none of whom have been small cats) the equivalent of one half of one large tin a day, split into two feeds. Ad lib plain wholebake biscuits, sure, but if you are feeding (and they are eating) Go-Cat or similar 'complete diet' biscuits, then the amount of that they are eating should reduce the tinned meat pro rata.
I did have one very greedy cat who would pig out on plain terrier meal (pretty much anything in fact!) so I had to restrict those too, but all my other cats have liked the Pedigree Mixer Biscuits (the ones with the roast fat coating -
) and eaten a modest amount so I've been able to leave a bowl out for them to pick on at. When they start cleaning that bowl out and miaowing for more is when I know they probably need to be wormed!
I've lost track a bit, but is Toby 6 months old now? I think I would have had him on a kitten ration up to 6 months; just like puppies they need more protein in the early stages. I also read once and have always followed the advice that kittens should be introduced to raw meat - but if they are hunting I suppose they're getting that themselves.
They sound as if they are doing great, anyway!