It is normal for a baby to suckle. This is how he/she relaxes and feeds. As your child nears 2 or 3 years of age, the less they need to suckle. If this is not the case, the use of a pacifier is recommended rather than thumb sucking.
Because YOU can control when and how your child uses a pacifier, but not his/her thumb. Never put sugar, honey or corn syrup on a pacifier. This may cause cavities.
It is best if your child stops sucking BEFORE 3 years old. If a child continues to suck his/her thumb or pacifier after his/her permanent teeth have appeared, the growth of his/her jaw and the position of his/her teeth could be affected.