Know the developmental stages of infants and children.  A good summary can be found in the Denver Developmental Screening Test, which breaks down development graphically into several areas, such as gross motor, fine motor, social skills, and language.  It is probably a good idea to memorize the following milestones: (remember these are AVERAGES with a wide range of normal)

 Motor:
  rolls over                     4 mos
  pulls to sit                    5 mos
  stands with assistance  8 mos
  pulls self to stand         9 mos
  walks                         12 mos
  walks up steps            14-21 mos
  rides tricycle               2.5-3 years
  juggles                        2nd year of medical school

 Fine motor:
  follows to midline      1 mo
  follows past midline   2 mos
  grasps rattle              4 mos
  neat pincer grasp     12 mos

 Language
  turns to voice             3 mos
  imitates speech          6-9 mos
  3 word vocabulary     12 mos
  200 word vocabulary  20 mos
  follows directions       22 mos
  knows arcane
   latinate roots             1st year of medical school