Most children in my reception class wear polo shirts, so the buttons are not really an issue. Where children do wear shirts with buttons, we either ask the parents to let them wear polo shirts on PE days, or teach the children to undo just the top two buttons and take the shirts off over their heads like a t-shirt.
Personally, I don't have a problem helping children with top buttons. New shirts at the beginning of the reception year invariably have really stiff top buttons. I struggle to undo them, so there's no chance of the children undoing them .
We do ask parents to spend the summer helping their children become as independent about undressing and dressing themselves. Taking sweatshirts off and putting them on again is a great thing to teach your child. It also really helps us if you teach them how to turn their sweatshirt back the right way in again.
Shoes are important, and we encourage parents to choose velcro shoes, or other shoes that their child can do up independently. In my first class, I had 10 children who had lace-ups and couldn't do them up themselves (obviously!). It used to take ages to do everyone's shoes up after 3 PE lessons a week! Even if your child can't do up their shoes themselves, try and teach them how to put them on the right feet. I'm constantly amazed that children can't "feel" when their shoes are on the wrong feet.
LIZS is right, zips are also a great thing to help your child learn to do. Try and imagine getting 30 children ready for playtimes and lunchtimes when you have 30 zips to do up!
Please don't worry if your child can't dress themselves independently by the beginning of Reception. Children all develop these skills at different times. Just try and give your child as many opportunities as possible to keep practising!
Oh, just another thing! If you have a dd, dress her in socks on PE days - tights are really, really hard to learn to put on!
Sorry for the really long reply.