Well, I did ask him! He was about 5 at the time. I called him into the kitchen and asked him what jelly he used, and he showed me the ketchup bottle. Incredulous, I asked him why he used the ketchup and not the jelly. He said he couldn't open the jelly. And besides, ketchup is a lot like jelly, they both sit in the refrigerator door shelf, the both go on bread, they're both pretty colors, they both pour/spread. Not a bad substitute, but not for me.
God Bless 'im, I was really proud of his lateral thinking and his refusal to quit when the first obstacle came up. And although peanut butter and ketchup is a good fit in this thread
for me, he had no problem with it. No preconceived notions to overcome. Of course, like a lot of kids, ketchup is a choice condiment. Sometimes his portion size for ketchup transcends "condiment" and approaches "side dish".
And the nice people in the New Jersey State Legislature would be just fine with that, since tomatoes are now the official state vegetable. Anything to get the kids to eat their vegetables.