To make the game simpler for very young children:
Use only one die. Use the color die and make matches just by color. Wild die matches and color. Or use the sea creature die and just match the creature, regardless of color. Lucky Catch is wild and matches any creature.
Use only the sea creature tiles and set them up in four rows of four. Don't use the old boot tiles or the treasure chest.
Allow each player two chances each turn to match the dice combinations they rolled, unless they roll Lucky Catch, which matches any tile.
To simplify and reduce competition:
Fish only in the sea or your own catch. Don't fish in other players' catch.
To make the game a little more competitive:
If you fish in another player's catch but turn over the wrong tile, that player can take any of your tiles, including the treasure chest.
Before setting up the game, draw one sea creature tile. All creatures of that type of color are worth 2 points. That exact tile is worth 4 points. Be sure to mix up the tiles well before you build the Lucky Catch Sea.
For example: You draw a blue octopus. At the end of the game, all octopus tiles are worth 2 points. All blue creature tiles are worth 2 points. And the blue octopus tile is worth 4 points.