My daughter is 9 months old and has never slept through the night without waking and calling me maybe 3-4 times a night.
Recently I have began noticing that if I put her to bed when it's 7pm her 'normal' bedtime and she's not necessarily exhausted she will take longer to go to sleep but generally stirs less in the night.
other nights when she drubbing her eyes and doesn't always enjoy her bath (she bathes every night before bed) she'll fall asleep as i feed her and usually wake around 3am for almost an hour.
Is your bedtime the same time for your children every night? and are they always 'ready' for bed?