Kew Green to Orchard MRT takes about 35-45 minutes by bus 14. My children & I do it every morning. We leave at 6:55 and get there by 7:50. I could leave later, but unfortunately the buses aren't as realiable as they would like to think they are. We have also taken bus 14 to Tanah Merah MRT and found it to be about the same time wise. At least on the bus you are guaranteed a seat. Even at the that time in the morning, I don't get a seat onthe MRT. Locals aren't very helpful with giving up a seat for an older person,(45+) or a person with several bags. Thus we bus it.
I think you need to consider the age of your children--mine are teens.
Most schools offer a bus service with another adult on board to help the children.
Good luck!
