WhosPickle - it really depends on your DS. My DS understands quite a lot of language so I'm able to tell him to stop doing something and generally he will stop. If he doesn't, I'll step in and stop him myself and then I'll usually distract him with something else or comfort him if he's upset about being stopped. But I don't punish, shout or smack. Discipline at that age really does mean "teaching" and nothing else - ie I'm around him in any situation that he isn't able to deal with (such as a big toddler group, out at the park etc) and I guide him at any point he has trouble. If he's managing fine then I step back until he wants me to play or needs help.
Threeleft, if his behaviour in the park is a real problem then you might have to stop going there until he can handle it better. What sort of things cause an issue when you're there?
The only reading I can recommend really is the "The Blank Slate" by Steven Pinker. He's a developmental psychologist who writes about human nature and in it there is a lot about the development of children. It's quite technical and hard going but it gives a lot of insight into how children's minds develop.
Really though, reading isn't necessary. The main thing is that you realise that you are your child's teacher, not their controller. Your aim is that they can handle the world around them in the most sensible, safe way. Sometimes they'll do things that piss you off. There will be a reason why they're doing those things, and the reason won't be to piss you off. They love you, you're their entire world, and mostly all they want is your love and attention. Yes they can be bloody infuriating but that's not their fault, they haven't learned yet how to manage things and they make tonnes and tonnes of mistakes. That's what learning is about. If you convey the impression that you're in control, that you have everything sorted and you have high expectations that you expect to be met, then your child will trust you. They'll still challenge you, but they'll know that you won't lose your rag because you are mum and you know what you're doing.
IMO the best gift you can give your children is trust. Be the one they can trust to sort things out, and to never hurt them or humiliate them.