Well I know all the medics will have a medic opinion but I will give an engineering one....
All bits of the body have a natural frequency which if you get vibrated it will annoy relavent parts of the body. If you know which freq to pump out you can shut a party down in 20 mins with all the girls going home with period pains by pumping it out next door with a freq generator and amplifier. Highly illegal I might add but it does work and unless they have some hot recording gear impossible to prove. You can give everyone the runs as well but thats a bit dodgy because they freq range is alot wider and also just inside the audio range.
Unfortunatly small peoples stomachs have the same freq as a cars suspension system and also some modes of ocsillation of an aircraft. This is a completley different mode of sickness that motion sickness which is a ear, eye miss match. You can change things by loading up with food or starving them. This is why most kids grow out of car sickness and why french cars are good for small kids. There suspension is that soft it's natural freq is that low it doesn't effect them but it is rubbish for infants.
If its got to the stage of mind over matter there is not alot you can do. Ginger beer helps some people others not. In mind cases you could give them a stone to suck as long as they believed it was going to help it would.