Hello there!
#1 Strategy
They could constantly ask them, their day, how they've been doing. And the thing's that they have been going through, either at school or other informal locations.
#2 Strategy
Another thing that can be used, you could perhaps give them a cell phone, to always be in touch with him/her and always be communicated.
#3 Strategy
Make sure that you are talking to them at a correct time. Don't give them a hard time as they are not feeling in a mood that is not pleasing. By you doing this, your communication would improve with your children.
I hope this helps you greatly!