M.M.
Actually, the sidewalk is city owned, it is for public use. I'm not sure about scooters or mopeds being allowed. In regards to moving for a bike - where do you think the cyclist should go? Of course you have to move out of the way when they are riding thru. As for leaving toys on the sidewalk - you just need to think about safety. Don't clog up the sidewalk, people need to able to ride thru on their bike or walk thru without having to step over them. If someone were to be walking/riding by and tripped/fell on a toy you may/could be liable.
Next time take the high road when someone rides by. Don't use the 'I was there first' card - kinda childish :(
I know these aren't the answers you wanted to hear and I understand your frustration about how close the girls have come to your kids. In that situation, you could speak to the parents. They may not be aware and may appreciate the feedback - or not :)
Here's my kum bay ya statement - everyone has to work together to get along in a community setting such as yours. Continue playing as you have just be aware of others and share.