您是否尝试使用mouseenter和mouseleave而不是mouseover和mouseout？即使使用子元素，它们也只会触发一次，并且自1.6.1开始，Prototype 支持它。

Did you try to use "mouseenter" and "mouseleave" instead of "mouseover" and "mouseout"? They will only trigger once even with child elements, and Prototype supports it since 1.6.1.