My son and I did it in Hawaii and loved it. You don't have to leave the surface if you don't want to, they let you go at what you are comfortable at.
I was surprised at my own reaction to this. Now, I went through the entire SCUBA diving program and got my NAUI certification in 1977, and spent a month in Hawaii taking a college marine biology class that had us doing 2 and 3 dives a day for the month. No problem. Fast forward 30 years, and it took me about half the SNUBA dive to feel comfortable doing down to 20 feet. The air lines are only 25 feet long, so you can't go any deeper. Now my 20 year old son,who had never done anything snorkeling, had no issue at all.
Funny how you change as you get older.