Your nephew is very lucky to have such caring and concerned relatives. I imagine it must be very frustrating for you to spend quality time with your nephew as he chats away with no idea what he is trying to communicate. This is a challenging experience, and I think that it was appropriate for you to raise your concerns with his father.

As you may know, by the end of their fourth year, most children make significant gains in speech and language. They can typically understand most sentences, use 4-5 word sentences, and most strangers can understand their speech. However, you have probably heard, that there is a great deal of variation in the development of children. While it is true that, for most children, strangers (and relatives) can understand their language at age 4, there are some children who may take a little longer. However, if your nephew is still not easily understood at age 5, his father should consider taking him to his pediatrician to discuss his concerns.

That said, I understand that this issue has created a rift in the family. If you feel comfortable, you may consider calling your brother (brother-in-law?) and let him know that you are saddened that this issue has created problems in the family. Let him know that you love him and your nephew, support his efforts, and believe that he is doing a fine job parenting (if you truly feel it). I imagine relationships will be slowly repaired once the dust settles.

For more information on typical language milestones, take a look at the following articles:

http://www.education.com/reference/article/Ref_Language_End_3_4_5/

http://www.education.com/magazine/article/Small_Talk_Language_Milestones/

Good luck!

L. Compian, Ph.D.
Education.com Expert Panel