I would avoid any literal reference to whatever sports their kids might practice. This "soccer mom" thing is very American and does not translate at all out of here. Un día de estos se va a gastar, lo mismo que Yuppies, Buppies, et all. Una madre de un muchacho que juega balompié es una cosas muy diferente en Wichita, Kansas y Morelos, México. Incluso si la traducción es hecha para una audiencia hispana dentro de Estados Unidos, en realidad lo que importa es que se trata de madres suburbanas relativamente jóvenes. (El hecho de vivir en los suburbios automáticamente asume su estátus de clase media, así que no estimo necesario especificarlo.)
Buena suerte

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Note added at 37 mins (2003-12-01 19:15:47 GMT)
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I might want to add that whatever sports the kids of these moms play is totally irrelevant for the purposes of demographic classification.
What does matter is that they are relatively young, usually in their 30s (because older kids do not play soccer in the US), and middle-class (because they live in the suburbs). No need to confuse the foreign reader who might not be familiar with American society with references to a specific sport, who is the passion of untold millions around the world, but only a mild athletic passtime for middle-class American pre-teens and teens, who most likely will abandon any interest in the sport once they reach senior high-school.