When I got home tonight the nanny was very excited. She had taken Middle Son out, and when they got in the car to come home, Middle was having trouble with his seat belt. He reached from the back seat and tapped her on the shoulder. She asked if he needed help, and she said he said "hea" and signed yes. She was startled that he was vocalizing, and asked again. Again, he said "hea" again.
The first speech-like response Middle has given in a VERY long time. Hopefully it's the start of a trend.