Hello @axartb - and welcome to the forum.
There are several places with calm waters perfect for children. You might consider other deciding factors before you settle on a spot.
WEST BAY
Your initial thought of West Bay is spot on. West Bay is world class by any measure. Further still, you’ll have the most options for water activities. The drawback is that it is a little more expensive than other areas. A good hotel to consider here is Paradise Beach Hotel, Infinity Bay, and Grand Roatan…(these hotels are in ascending cost order).
HINT: locals eat at restaurants not on the waterfront and spend less money to do so.
WEST END
West End is another alternative. The waters in HaBayMoon bay are totally calm and clear. Snorkeling is not as good as further out in the lagoon you’ll come across more seagrass than you will coral reef. BUT, there are more eateries and it is more lively. West End is a little more commercial and vibrant…overall cheaper hotels. Unlike West Bay which was known for being the “resort” alley.
HINT: You can take a water taxi to and from West Bay and West End all day long and deep into the night. So you could come to enjoy both locations on the same visit and on the same day.
I hope this helps. Let us know if you any other questions!