I love both Kidani and Jambo House, so it is difficult even for our family to decide sometimes.
The 3rd bathroom is terrific. Our last trip we had 4 adults and 4 young kids in a 2 bedroom at Kidani. The bathroom was very helpful.
Kidani's lobby and common areas are smaller, more intimate. I personally liked this. It felt more relaxing to me.The kids loved the Community Room. The gift shop is super small, but this meant I was less tempted to spend more. When I stayed at Jambo I walked through that shop every day and always found more things to buy. We stayed at Jambo during the Christmas season and the lobby, tree, decor was breathtaking. I also enjoyed ordering room service from the Jiko menu.
The pool areas at both are very nice, but different. We tend to use the one we are staying at, but try the other one once or twice.
We tend to buy food and eat our own food when we are at the resort, so lack of counter service isn't a deal breaker for us. If you plan to eat at the Mara on a regular basis, it might be annoying to have to travel from Kidani to Jambo. We only made the trek once. We also ate the pool bar at Kidani (good sandwiches).
The park buses picked up Kidani first, so we pretty much always got a seat.
Both had fun activities for the kids. 5 yrs old would be a good age to do the bead activities.
Both are awesome places to stay. It is really a matter of your opinion & priorities. Honestly, I don't think either would make for a bad vacation.