Looking for Free Websites for Developing Language Skills

The other day I was meeting my friends and their children. I noticed that while playing with "Jake", He was "slinging slang" and missing some prepositional phrases from his sentences. I felt his language skills were "underdeveloped." The family is big on the use of technology, so I was wondering what are some websites or technological tools for the parents that would help develop Jake's language skills. He currently is in 5th grade. Thanks for your thoughts!