It's very contagious, but if it's you who got it first, not your dcs, then you stand a far better chance of avoiding them getting it - by constant hand washing, toilet cleaning, surface cleaning, etc, if you can actually cope with that when you just want to die... And don't let your husband pour a sick bowl down the sink right next to your toothbrush, or you'll find yourself getting the symptoms again after you thought you'd recovered... (Why he couldn't use the toilet for disposing of it, like a normal person...).
As for how you feel, it depends on how badly you get it. Generally pretty awful for several days, with temperatures, vomiting and/or diarrhoea, although some vomiting bugs are only 24 hour things, where you feel shite for 24 hours then a bit weak and achey for a few days more, rather than very ill for 3 or 4 days and then weak and achey for another 3 or 4 days....
You have to be very careful if your dcs get it. My ds2 got it REALLY badly when he was 2 - the vomiting didn't last long (about 24 hours), but within seconds of drinking anything, you would hear an awful gurgling noise and brown water would exit from his bottom. He ended up in hospital on a drip for 3 days, so it can be serious if they really can't keep in water and rehydration salts/flat cola (tastes A LOT more pleasant and pretty much as effective).
If your children do get it, don't make the mistake of giving them food too soon after they start looking like they're getting better, or you'll prolong the vomiting and diarrhoea by a couple of days. I've made that mistake a few times when my dcs have been ill with d&v. Basically, they don't know what's good for them and start trying to eat things a day early...
Oh, and don't wait very long to see a doctor with a 5-month old (or a 20-month old, come to that), especially if they can't seem to hold down little, but frequent, sips of water (and pref. dioralyte or its equivalent) as severe dehydration can actually come on quite rapidly in small children.