My child's development

Should I worry if my child's development does not correspond to the ages given in books ? When will I know if my child is right or left-handed ? Why do 5-to-6 month old babies put their feet in their mouth ? My 12-month-old child does not walk. How can I stimulate him to take his first steps ? My 2 year old yells and get angry when other children approach his toys. How can I help him to share ? Why do 2 year olds have so many temper tantrums ? Is it normal for my 3½ year old to talk to a non-existent friend ? How can I appease my child's fears ? At what age can my child start eating with a fork ? At what age can I safely give my child scissors ? ... and many other questions !