Returning to the US will require that you have valid visa stamps it your passports.
The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.
Leaving the US and then returning will do nothing with respect to your family's I-94 date. They will need an I-539 filed on their behalf. On the application, make sure you cross reference to your H-1B.
This post is not legal advice, and does not create a lawyer-client relationship.
There are two ways you can extend your family's I-94 cards -- file an I-539 for your spouse and list all children (each will get a new I-94 card). This must be filed before the expire in September 2011 and make sure each passport is valid for at least six months. You need to include copy of your H-1B approval, marriage and birth certificates and evidence you have maintained status such as W-2 and current pay stub. Other route is for them to leave the U.S. and schedule a visa interview at an overseas consulate.(the Mexican consulates are NOT inclined to take third-country nationals these days so check before you go; may be better with a Canadian consulate if you do not want to go to home country.)
Lynne R. Feldman, Attorney at Law
Concentrating in Immigration and Nationality Law
2221 Camino Del Rio South, Suite 201
San Diego, CA 92108
phone: (619) 299-9600, facsimile: (619) 923-3277
Formerly Adjunct Professor -- Immigration law
University of Illinois College of Law