With the grand kids that are about that age I find the following handy
Choose a spot close to home that has restrooms.
Make the trip in the morning on a sunny day, and limit fishing to about an hour between breaks.
Take snacks and cold drinks with you and a coloring book (nature related).
Have the kids take breaks from fishing and give em a minnow net and pail to have fun.
Life jacket that fits.
Pack a first aid kit.
Bring a hat and sunglasses.
I often go to the dollar store and pick a few fun things up to occupy them when the fishing bug fades, which is usually pretty quick.
Don't count on fishing yourself, this is an adventure for the little ones and don't forget that.
My own very fine arsenal includes, the Shakespeare Princess and Barbie Fishing Kits, and of course the ever present Batman Backpack Fishing Kit.