They need to hear lots of different words, and they need to be given a part in conversations. Sudden, loud noises startle babies and cause them stress. Stress blocks learning. Your child will grow and learn more quickly if your home is calm and free of sudden loud noises. Your child is different from all other babies, and he will develop at his own rate.
Children roll over, sit alone, crawl and walk at different times and ages.
Don't be too concerned if you child's rate is different from those shown on this site. If you suspect that your child may be falling far behind in learning the Start From The Smart skills, talk with your baby's doctor about your concerns. These early years lay the foundation for all further learning.