My son decided to teach his son ASL when he was turning 2. It seemed to switch on the light - words and actions were connected! His spoken vocabulary increased by leaps and bounds as his ASL vocabulary expanded. He got used to watching us make, and then explain each gesture. So, I turned one day to realize he was watching as I scratched an itch - and had to explain that this particular sign means my nose itches!
Our youngest was a late talker and we used a lot of ASL to communicate as well. He communicated so well with it that we knew everything was OK mentally.
His speech development had been normal until 18 months when he had a serious bout of RSV. After that he really regressed.
Fortunately he had a young friend who LOVED to sing children’s songs. The singing really brought my son back around to being verbal. As some others have commented, since then we can’t shut him up.