Because you asked the question --- "Is it worth the money" ---- I think that you really have to consider the diners and their preferences in order to decide whether Jiko is worth the money.
Although children are certainly welcome at both locations, I would venture to say that for most children, you'll get a better value for your money at Boma. Even my own "child", age 22, couldn't care less about a place like Jiko and it wouldn't be worth spending our money for him at Jiko.
If the people in your party prefer more simply prepared food, or strictly American food, or aren't adventurous eaters (nothing wrong with any of those things), then Jiko won't be worth the money.
Have a look at the Jiko menu. If the menu items look intriguing to everyone in your party, then go! Whatever is on the menu will be well-prepared and will be worth eating. And the service is impeccable. It is top-notch, it is attentive, but it is not stuffy.
For my husband and me --- Jiko is definitely worth the money. Love the unique experience and the unique food.
If I could only choose one restaurant?
Jiko, if it is only my husband and me.
Boma, if it is husband, son, and me.