It is important to establish regular routines with the babies that are meant to promote longer periods of sleeping. If this is not happening, perhaps you are expecting too much or possibly your baby does not need as much sleep as other babies.
Some specific suggestions I can make include insuring a calm, relaxing bedtime schedule that is routine and happens regularly at about the same time each night. Reading a book, low-key play, and even one last feeding are all suitable during this ritual. Be sure to put the baby to bed in the same crib that will be used for the whole night. It does not help to have the baby fall asleep in one place (e.g. your bed) and then be moved to his crib. Placing him in his crib awake and then allowing him to fall asleep can also make a difference. Since significant variations can be problematic, consistency by all caretakers is most definitely a plus. I do recommend the Ferber method (best discussed in his book Solve Your Child's Sleep Problems ) for encouraging your baby to learn to fall asleep and stay asleep.