You were interested in them when they passed you often, right? Well why don't you swing it the other way and pass them a lot (riding a bike or something to post a letter, visit shops, hang with friends, cycle for the fun of it, etc) and soon they'll want to know more about you as well. Then they might (if you're lucky) go up to you and start talking. Or you could just casually say hi when they come past you! That would work easily! But don't sound too eager. Remember - they are just strangers so it's probably best not to start giving them big hugs and talking to them like they're your best mates and stuff, because chances are they might feel quite shy and embarrassed.
Also, don't approach the ones that are smoking in the corners in their black hoodies (although this tip was a bit obvious!) Just talk to the nice-looking ones who are smiling. If your neighbourhood is not very safe and your parents like to be with you when you're out, you could always ask them if your whole family could stop by at the neighbours house, to say hi. Or your family could even invite their family over for tea or something. Then you could get to know a girl your age. Start off with a few friendly waves first, and then invite them round. If you don't hit it off, don't worry. You can just stick to the friends you had before. At least you tried and hey, it was an experience. But there's always the chance that you could really like each other and become great friends. That would be the best thing that could happen, and you're just back to where you were before if you don't like each other. Go on - you've got nothing to lose! You might as well make the first move, because it sounds like great fun to be able to know lots of the kids in your neighbourhood, and you can go round to their houses when you're both free and things like that. Go for it! ^ _ ^
