No advice here but some pros/cons to weigh:
If the trip is planned for the May/June 2009 timeframe, consider whether you are willing to deal with any of the possible hassle from a new resort opening (Kidani.)
If you like Boma, Jiko or Mara, consider Jambo. The walk between the two is substantial and Kidani will not have any counter service restaurants.
The rooms at Kidani are larger and have the extra bathroom in 1B / 2B.
Kidani will have a water play area by the pool. Sounds like your kids may still be on the cusp of enjoying something like that. But the Kidani pool itself looks to be MUCH smaller than Jambo if the are just looking to swim/float/splash in the water. Both have slides.