Not every child develops at the same rate, and it may not indicate a problem if your child is behind on one or two milestones.
Most children do speak 5 or more words by 15 months. As I understand it, though, it isn't particularly uncommon for children to be a bit behind on this.
Perhaps more troubling is your statement that your son doesn't seem to understand anything you say, either.
Does he use gestures besides mimicking what you do? Does he point when he wants something? Reach for you when he wants to be picked up? Wave good bye? These are all forms of communication that are indicators to look for.
Warning Signs of a Possible Problem
If you're concerned about your child's speech and language development, there are some things to watch for.
An infant who isn't responding to sound or who isn't vocalizing is of particular concern. Between 12 and 24 months, reasons for concern include a child who:
isn't using gestures, such as pointing or waving bye-bye by 12 months
prefers gestures over vocalizations to communicate by 18 months
has trouble imitating sounds by 18 months
has difficulty understanding simple verbal requests
Even if your son is using gestures to communicate, you may want to mention his vocabulary to your pediatrician. Even if there is no cause for concern, it will provide more reassurance to hear it from a professional.
As for what you might do to help your son learn:
- first and foremost, talk to him. Use full sentences, and talk about anything and everything. Most of early language development comes from the child listening to adult speech. The more you say, the more he learns.
listen to what he says. When he babbles at you, listen quietly, then respond as if he had just said something very important. Make up in your head whatever you like for what you think he said. It doesn't matter if you pretend he was discussing politics or the events of the day, but responding as if he said something meaningful models conversational behavior, and helps in the learning process.
Read to him. The more you can read to him, the better. If he doesn't have interest in books, make up stories. Just so long as you are talking to him. The more he hears you talk, the faster he can pick it up.