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. …