The admonition to avoid tickling a baby's feet is based on a myth. The origins of the myth are unknown, but the reason given for not tickling a baby's feet is that it can cause stuttering when the child gets older. This is untrue.
According to Dr. Laura A. Jana, a columnist for Disney's Babble.com, stuttering is not caused by tickling, although the true cause of stuttering is still unknown. Stuttering is more common with boys than girls and usually begins occurring in a child's speech pattern between the ages of 2 and 4. Studies indicate that genetics play a role in whether or not a child stutters.
There are many so-called "old wives' tales" that surround having babies and rearing children. Some of the advice for parenting has been handed down from generations past when life was quite different. Consequently, many of the older beliefs and warnings are outdated as well as questionable in terms of having lack of verifiable proof. Some people are well aware that certain information is based around old myths or folklore, but they follow the advice anyway because it is rooted in cultural or family traditions. It's generally best to take unverified facts with a grain of salt when it concerns the health or well-being of children.