That possibility is so remote it is nil. The kids got up at 6:30am, and even if we stretch the time to think she didn't eat breakfast until 10am, and she got home at 10pm and we don't know when she died...well that pancake was long gone RS.
Besides, the Ramseys never said anywhere that either of their kids ate anything at all that day with the exception of Burke eating "a bite" of breakfast. They give a very loose timeline of when they got up, mentioned what was made for breakfast, said PW saved a plate of crab, and denied any knowledge of the pineapple. The reason nobody knows when JonBenet ate what is because the Ramseys never would tell anyone any time she ate anything for sure all morning, afternoon, and night! Since JonBenet was murdered, and they are supposedly all into finding the killer, one would think they would have known a few more facts since it is important to tie up the details. You gotta wonder what that is?