I know Vietnam fairly well after 4 trips there in the last 4 years. Honestly, it's not the safest place. Seriously, I would be concerned about any small boat cruise - even the very best would not be good enough for my kids (rarely will they have life jackets to fit youngsters). The other problem in VN are the roads - death traps in my opinion since they have the world's worst drivers in this country!

It's a great country, and I will be returning in 6 weeks myself, but not with children.

Go to some place like Luang Prabang or Siem Reap.