Hawaii? Dozens of Snorkel Bob locations can't all be wrong...
On Maui check out Kapalua Beach, Old Airport Beach, Black Rock or Wailea Beach. Kihei is probably the most affordable area to stay in - lots of condos across the street from the beach. vrbo.com lists hundreds.
Near Kona there's Kahuluu Beach Park. It's 5-7' deep for a very long way out. And there's turtles there always. Lots of affordable condo options in that area also - or there's an older Sheraton that's supposed to be decent.
Or the Poipu Beach area around Kauai. There's even a breakwater protected "Baby Beach". It's actually interesting, you can step over the breakwater but only the little fish get in. Just with a mask I saw a lot of baby tangs, angels etc. inside. It's the south side and shielded by the island so almost always calm. The problem with Kauai is that some of the other "beach" entries are pretty rough over lava. I don't go to Oahu - too crowded IMO.
Building on the post above there's a snorkel trail at Phil Foster Park in Riviera Beach also.
Phil Foster Park - 2 acres, 6-10' deep. You can also snorkel at the adjacent Blue Heron Bridge but it's really a better muck dive.
Off the gulf coast we used to snorkel off Siesta Key -
Crescent Beach there is called the best snorkel on the Gulf Coast. Didn't know that when we were there. I'd be hard pressed to name a 2nd site nearby though - it's a georgeous beach area because it's flat and sandy a long way out - not the best for snorkeling.
Or there's also the Keys. Lots of snorkeling but mostly from
boats. Some of it surprisingly is really shallow though - even farther out. I've stood up on a sandbar out so far I couldn't clearly make out people on the beach.
Florida Keys Scuba Diving Vacation planning | Florida Keys Snorkeling
There's also good snorkeling off San Diego in La Jolla. But that water is always cold - even in the summer it's probably a full 5-7mm wetsuit for a 6-year old.
http://www.kpbs.org/news/2007/jul/31/best-snorkeling-spots/
If you want to venture a little farther out see if you can get to St. Thomas reasonably. Coki Beach is a known snorkel site, it's shallow, they also do Snuba there - that has a 12' hose so they're seeing something shallow. Sapphire Beach nearby is another.
St. John - a 20min. ferry ride over - has Trunk Bay - there's a snorkel trail there. And several other nearby beaches have good snorkeling also.
Snorkeling St. John Virgin Islands There's a car ferry from the East End so you can "drive" over for the day - St. John is a lot pricier to stay on than St. Thomas.