Establishing good sleep habits for infants and toddlers is a job in itself, along with everything else a parent has to do.
All kids are so different. My son was the best sleeper until we had a flood a few years ago, and hasn't slept the same since. My daughter had night terrors until she was 5; waking up screaming at least twice a night, and no amount of consoling would calm her down.
Not sleeping well doesn't just affect kids, it dramatically affects parents. I know I am a much better Mom when I get the sleep I need. I know my kids are much happier and fight less when they get the sleep they need too. Being a sleep-deprived zombie is no fun!
Tuck has a Parent's Guide to Healthy Sleep which is full of great tips for establishing good sleeping habits for your kids. Check it out!