Turtles disappear

We have tried at least 6 times to get the turtles to work. Every time the eggs hatched there was nothing there. Read  something that said you have to be within 50 blocks or they will disappear. We did this and finally got some turtles and we fenced them in so they wouldn't despawn again. We even named them with names tags. Today logged in and 2/4 we're missing. Logged in a little later and all 4 are gone. I have had so many issues with the turtles I want to rage quit the game.