What's gooey on the inside and crusty on the outside?

My Pookie is in first grade now and attends public school. Sometimes it is hard for him to remember to eat his sandwich first. He regularly asks for peanut butter and Aunty Leslie's peach jam sandwich, milk, and raisins. If I pack goldfish, fruit snacks, or juice, he neglects his sandwich. So I tell him if he eats his lunch he can have special snacks after school. He asks me every day if I wrote a note for him to read in his lunch. Usually I take a page out of my planner and carefully write a note using D'nealian-- the type of handwriting he is learning in school. It usually says:

Dear Pookie,

I hope you are having fun today at school learning new things. I know you will remember your rules and good manners in the classroom and at recess. I will pick you up at 3:15 p.m. Be good.

Love,
Mommy

Today I took the opportunity to capitalize on his ability to read and his enjoyment of rhymes and riddles to brainwash him into eating the sandwich first.

Dear Pookie,

Today for lunch before you munch, you first must solve a riddle.
The thing to eat, is not a treat. Eat the food with jam in the middle.
It has isosceles triangles. There’s two of them—a pair.
And one more clue I have for you, these two things make a square.

The liquid you will be drinking is not juice – so you know,
The chemical symbol for your drink is actually H2O.
It falls from the sky, when weather’s dry and gives our plants a drink,
You wash your hands and dishes too, and your body when you stink.

One more snack, that I did pack, are packed in a little red box,
They are chewy and small and help you grow tall, they do not taste like rocks.
They don’t need to stay cold. I keep them on top of the place the keeps cold foods good.
California is printed right on the box. Eat them last-- as I said that you should.

I will come to your school when you are all through with your day of learning and fun.
I can’t wait to see, which boy waits for me, it’s you my first born son!

Love,
Mommy