The best way to stimulate speech and language development for your child is to READ and TALK! Pretty simple! Read to your child or have your child read to you. I encourage you to read everyday with your child. Talk to them about everyday activities. Model correct sound production and sentence formation as you discuss events throughout the day.
Here are some helpful links:
Speech VS Language: What is the difference?
NC Department of Public Instruction - Video describing Related Services (speech, occupational, and physical therapy) in school
Developmental Speech-Language Milestones (Pre-school Years)
Development of Speech-Language Milestones (Kindergarten - 5th grade)