Only thrift children are manage to fill up a money box.的确单复数不对应是个问题.这句话本来想要表达的意思就是节俭的小孩才能储满一罐子零钱.其实是把前面的children改称a child会比较好.
if fifty pence piece are not exchanged for sweets,they can rattle for months inside money boxes.
这句的话也是用a money box就可以了,更地道.当然用复数也不能说错.