I wouldn't ask the server to do it..but you could visit mara before your Jiko reservation, get the children meals and take them with you into jiko. The servers at Jiko are very busy, so not really fair to ask them to run all over the place.
Or..why not get the kids to try something new, in fact...the new kids menus when we had our granddaughter there a few weeks ago didn't even have nuggets in the nicer restaurants..it was salad, chicken breast, real food, good things for kids, not the cr*p food.