Here's some info I found, I had the same question because my daughter cries in her sleep sometimes, and it seems as if she were having a nightmare. Hope this helps.
We dream more in the first 2 weeks of life than at any other time. The visual part of the brain is more active during newborn REM sleep than during adult sleep. They seem to have more vivid visual dreams.
Infants 3 to 5 months old dream much more than infants 6 to 12 months old do. 18-month-olds dream almost twice as much as 3-year-olds do. By age 3, the amount of time spent dreaming per night is in the same range as that of young adults. As the wheel of time turns throughout life, each year we dream a little less (Science, 1966; 152:604).
at 1:19 PM on Nov. 21, 2008