I also do not think there is typhoid in Colombo.
There is dengue, though. Best precaution is to ensure you and your kids are safe from mosquitoes. Use some good mosquito repellents. You can also rub some local camphorated balms (eg., Siddhalepa). The strong smell keeps mosquitoes away.
As with any other part of the world use your intution to decide if a place is safe or not. It is generally safe to eat out in Colombo.
Have a great and enjoyable stay.