It depends on why he's waking and what you do when he wakes.
If he's getting molars, he'll wake up.
If he has a cold, he'll wake up.
He'll wake up from nightmares and night terrors.
If he gets too tired during the day (no nap, too much activity, etc), he will wake up.
If you rock him back to sleep, he will wake up to spend time with you.
If you scold him about waking up, he will wake up to spend time with you.
If you lay with him until he's asleep, sing him to sleep, allow him out of bed, read him a story, get him a drink, etc... he will wake up so you can do those things.
What you do about it is up to you.
Some let their toddler fuss (or throw a fit).
Some give in and figure the toddler will sleep through the night someday.
Some stay until the child is asleep, slowly moving closer to the door.
Some check back in every 5 to 10 minutes until the child is asleep.
Your choice. Do what works for bo
at 7:55 PM on Feb. 28, 2009