Is this a good Experiment for a Science presentation for a class? Has to be simple?

i have this science experiment to do for a fourth grade class. i teach fourth grade. i have to make a simple science experiment to show. what do you think i should i do? do you think i should do a lung experiment with a balloon deflating in a bottle? i think it's kinda bad. my partner/ helper Aidan is telling me i should do it but it was most likely his idea. please tell me! i need to do this for my class before the end of next week! please answer this as fast as possible and i will thank you so much! bye the way, people think i look to young. i don't know why. is that a bad thing? oh well, i don't care.