I have started doing some street candids recently too. I love the different look you get in peoples faces and eyes when they are completely oblivious to a camera present. By law, you are completely in the right by taking photographs of individuals frequenting a public place, but there are a couple of things you may want to coinsider:
1. Always be open about what you are doing. This doesn't mean you should intentionally reveal yourself to your subject, but just don't act in a suspicious manner. Using an SLR makes you seem more "honest" because you aren't using a small, concealable camera, and makes you (to most people who don't follow photography) seem like more a "professional".
2. If somebody turns and looks at you as you take their picture don't try and hide what you are doing. When this happens I keep eye contact with them and smile, maybe waggle the camera a little to indicate to them what I was doing. If they look at me before I take the photo I will hold up the camera and make a questioning expression. 99.99% of people will respond positively to this. They will smile back, or perhaps pose for you. Indeed, many people seem flattered that you would want to take their picture.
3. Children are difficult. It is very important that you don't come across as threatening to the parents. If I am in risk of being seen by the parents I will ALWAYS make eye contact with them and establish if it is ok if I take the photo. Often, if they are okay with me taking the picture, I will approach them and offer to send them prints by email. Having a name card of any description makes these people a lot less suspicious, and often parents are very happy to accept. It is important with children that you pick your place approriately. For example: photographing the kids playing in the fountain in Bugis Junction is unlikely to raise any objection and is perfectly acceptable. However, photographing a child playing on its own with its mum or dad in the HDB park is likely to be a bad idea. Just think about what you would be comfortable with and work with that.
4. Finally, if somebody does raise an objection I always find it best to talk to them, not to run off. I am always open and honest about my intent and if somebody questions my activity I will explain to them in open terms that the scene caught my attention and that it interested me as a photographer. I will ALWAYS offer to delete the picture BEFORE they ask me to. Most people will respond to this positively, fequently expressing appology for the missundersanding or indiference. In the end, if they do tell you that they are uncomfortable with your pictures and ask you to delete them I always do it, and it appears to apease them a great deal.
In the end, you want to take pictures that YOU are happy with, and that strike a chord with your memory of the event. Even if you end up "winning" a fight with a subject and keeping the picture, it will forever be marred by the unfortunate circumstance that you went through to get it, and you won't be able to enjoy it. Anyway, I hope this helps you. Happy candids!