How can I increase my child's appetite so he won't be skinny?

May be normal. Depends what you mean by skinny. Some kids are just naturally slender. After about 12 to 15 months of age kids only gain 3 to 5 pounds per year. As long as your child has a normal rate of growth and good nutrition it may be nothing to worry about. Also remember that giving sugary drinks and juices in between meals make your childs appetite decrease and they will not eat as well.