(This post originally appeared on Child Talk)

You may have already seen this very cute video of two twin boys having a grand time "talking" to each other:

These two are clearly enjoying each other and it is very sweet to watch them do so. And, in this case, the boys look to be very early communicators who are just having fun playing around with sounds. The video does spark an intriguing question though: Do twins really communicate to each other in their own secret twin language?

The idea of a "twin language" (or "cryptophasia" if you want to get really fancy) has been around for some time now. It's been reported that up to 50% of young twins will have their own twin language--one which they use to communicate only with each other and one that can not be understood by others outside their little duo. The theory behind this "twin language" goes a little something like this: twins are so close to each other and rely on each other so much that they don't have as much of a need to communicate with the outside world, so they make up their own idiosyncratic language that develops only between the two of them. It's a fun and almost magical idea, for sure. But does it stand up to reality?

It turns out that many researchers think it does not. Some research studies seem to indicate that what appears to be "twin language" might actually be two children with the same delay in phonology. Phonology refers to rules that children use to put speech sounds together into words. As I've explained in other posts, children tend to develop speech sounds in the same general order and they often make the same types of errors in their speech. Children with phonological delays have speech sound systems that don't develop as we'd expect, and this makes it hard to understand their speech. Some researchers now believe that what is often described as "twin language" is actually two children whose speech sounds are not developing as we would expect.

Researchers further theorize that these speech sound errors (the "phonological delays") are prolonged in twins because each twin has a partner who seems to understands him and uses the same type of speech as he does. While this does make it kind of a "twin language" (because the two twins seem to understand each other when others can not), it's also a delay in speech sound development that might need to be addressed by speech therapy. And in fact, studies have also linked the presence of a twin language to language delays later in the school age years.

This is not to say that parents of twins who have their own language should panic. There does seem to be a small percentage of twins who have both their own language and are able to communicate effectively with their parents in the "real" English language. These twins will switch back and forth between their own language and the English language, depending on who they are talking to. This type of "twin language" is not linked to later language delays. It's also, however, less likely to occur.

It's also important to note that researchers have not found that all twins who have their own language will go on to have language delays. Twin language seems to be a risk factor, not an absolute indicator the twins will struggle with speech and language. It's enough of a risk factor, though, that an evaluation by a speech-language therapist might be beneficial in helping decide what's really going on.

Bishop, D.V., & Bishop, S.J. (1998). "Twin language": A risk factor for language impairment? Journal of Speech, Language, and Hearing Research, 41(1), 150-160.

Becca Jarzynski, M.S., CCC-SLP is a pediatric speech-language pathologist in Wisconsin. Her blog, Child Talk, can be found at www.talkingkids.org and on facebook at facebook.com/ChildTalk.