There are two sets of side impact crash tests. One from the NHTSA and one from the IIHS. In short, the NHTSA uses a taller dummy in a vehicle being struck by a car. The IIHS test uses a shorter dummy in a vehicle being struck by something similar to an SUV. Both tests are equally valid, but the IIHS test does put more emphasis on head injury. Side airbags with head protection will be more of a factor in the IIHS test. Ideally, you would like a vehicle that gets good ratings in both tests. The IIHS test is relatively new, so not many results are available. As Ulrike said, most vehicles with side impact airbags for head protection do score well in the IIHS test.
Many people remember the issue with frontal airbags in the early 90s. The first ones deployed with a lot of force. At the time, it was much more common to let kids ride in the front seat, too. The combination led to a number of fatalities. Many people figure side impact airbags will be the same. In fact, there isn't a single death yet attributed to a child passenger from side impact airbags, and only one to an adult. Risks from side impact airbags are associated with passengers who are unrestrained or those who are improperly restrained. The risk is also greater in older vehicles with early side airbag systems for the torso. Newer vehicles with side impact airbags for the head (like curtain airbags) comply with a set of voluntary standards and have been tested with out-of-position dummies in many extreme seating positions. These newer systems should pose very little danger compared to the protection they may provide.
It may well be true that kids in a 5-point child restraint gain little benefit from a side impact airbag. On the other hand, adults and kids in boosters should gain a significant benefit. I can't comment on removing passengers with a deployed airbag, but I suspect I'd rather be able to help the EMT get out from a deployed airbag on my own power than have to be removed with serious head injuries.
The very short answer is to make sure all passengers are properly restrained in seat belts or child restraints with kids 12 and under in back. That alone will keep your kids very safe. If you can buy a vehicle with good ratings in all the crash tests and a full set of advanced safety features, your family will be even safer.
Also:
http://www.car-safety.org/carguide.html
http://www.suvsafety.info