Children reach developmental milestones in how they play, learn, speak, behave, and move in their own time, but there usually occur within a reasonable expected time period. If they do not it is something we should be looking at further. Although I see your child regularly, as a parent, you know your child best. In our conversations about your child I will raise any areas of concern I might have, however if you think there could be a problem with the way your child plays, learns, speaks, acts, and moves talk to your child’s doctor immediately. Don’t wait. Early intervention is very important.
How to Help Your Child (pdf)
Having access to a quality developmental checklist is important. The link below from the CDC I think provides not only the developmental milestones, but also key areas of concern to be aware of.
Ages covered are 2 months through 5 years. There are direct links for each age as well as a link for a complete milestones checklist which can be downloaded. All resources here are free.