Some quick suggestions:
1. Make sure you check to see what is legal
or allowed in your location.
2. Use live bait.
3. Use artificial fish
4. Teach them how to cast a throw net (where legal) for your bait fish
5. Buy a crab trap, and have it on the bottom while you are working the rods. Even if you don't catch something edible, you might still catch something interesting for kids
to see, before you return it to the sea.
6. Take a big plastic or glass magnifying glass with you and a field guide to local fish and marine
life, including crabs. Even if you catch something small or inedible, make it fun to identify the fish or animals
if possible by matching them to what is in the book.