Make a routine. After putting your children to bed wait three to four hours before waking them up very briefly to go to the bathroom. Take them to sit in the bathroom even if they don't have to go. Eventually they'll be conditioned to go at night themselves.
I suggest using pull-ups at night to protect beds and pride. Take them to use bathroom before going to bed an again in the morning as soon as they get up. Do this even until they are completely potty trained for night.