No. As I said, other children were detained at Guantánamo. They were detained in a special facility called Camp Iguana and afforded special age-appropriate treatment. Omar appears to have been singled out.
There is one other individual whose case is pending before a military commission and whose age is not well known. The government says that he was 17 at the time he engaged in hostilities against the United States, but I don't know if that's been proven as a conclusive matter, and there is some indication that the government charged him for no other reason than to deflect the critique that Omar was being singled out and was the only child soldier being prosecuted by the United States at Guantánamo.
So certainly Omar's case, and his age being 15 at the time, is unique and significant as compared with other children's cases at Guantánamo.