介词引导的地点状语前置,主谓要倒装.on the side walk (in front of one of the stores)是状语,括号里面的是限定性短语,意思是：人行道位于其中一家商店的前面.
整句话的意思是：一排商店中一个商铺前面的人行道上,有一个男孩哭的很惨
正常的语序是：
A litter poor boy sat on the side walk in front of one of the stores,crying bitterly.
举个例子,In the tree was a nice bird.
On the street lies an old woman.