Hi,
I would also recommend Kiettisack School. The overall population is greater in girls compared to boys. It has a large Korean population as well but there are also many expats from Canada, US, UK, Pakistan, India, Vietnam, China, Philipines, Japan, New Guine, and others.
The school has a very strong teaching staff particularly in the primary grades and into the Junior Secondary.
I think if you research and look around you will find that while there are many schools in Vientiane the top choice is Kiettisack for a number of reasons. Should your children need ESL/ESC to acquire English skills, I personally don't know of a better program in Lao.