Don't bother teaching your children how to tell time. Oh no. Just get them one of tehse Kidsleep nightlight alarms and they can easily discern when "sleepy time" and "wakey time" is.
Simply look at the clock face, and the sleeping rabit or wide-awake rabbit will tell you exactly what you should be doing right now. The best part of this clock would be if your kids regularly wake up at 4:00 am, the sleeping bunny would tell them not to stay in bed and not come and wake you up. Yeah, that'll probably work until 4:30 am.