Water probably won't be the main problem with the finishes you're likely to consider. Fruit juice and red wine are the real problems.
Osmo will resist them for a good few minutes, but I've done tests with some cr@ppy water based pu varnishes that saw the wood stained in under a minute! The difference between brands is pretty startling. If you really want a bomb proof surface you need to think about two part finishes, nothing else can really compare to the level of protection that something like Rustins Plastic Coating delivers. Otherwise I'd suggest thinking about a finish that's easy to remove and re-apply every couple of years...or when the kids have grown up!
Good luck!