Chiang Mai - Khon Kaen

A group of us from Chiang Mai are thinking of going to the Khon Kaen marathon in January. We have never travelled to Khon Kaen before and don't know what the options are. Our current thinking is to take Nok Air from Chiang Mai direct to Udon Thani. Since there will be up to 6 young kids travelling with us, we want to make sure that the trip is relatively easy and quick. What options are available for travel between Udon and Khon Kaen? What is the approximate travel time?

Thanks for any tips or advice.