Hi Chloe,
Heres what Andrew and his Diabetic friends do, and contrary to belief you can eat sweets in moderation, preferably after meals, before going out to play or doing other activities. Some of our neighbours know Andrews Diabetic so dispite the costume , usually give him fruit/nuts or 50p. When he returns home with his goody bag we sort through them. Really sugary sweets go into the "hypo" jar (for emergencies) others go into a "treats" jar, and 3 days a year we allow him to run a little high (halloween, birthday and christmas.) You'l find in time and according to your insulin regime when you can have treats. Your Diabetic nurse will help you, and if like us you like chocolate, go for a higher cocoa content as they contain less sugar (Lidl's do fantastic small bars , pack of 5) You'l find before P.E at school you'l need a carbohydrate that helps with the energy you'l burn up, milky ways are good, but always check your blood before and after, in time you'l know what works best for you, Andrew has a couple of biscuits.
Hope this has helped a bit.
Keep asking, and we'll try to answer
take care
Suzi x