Dd1 (5yrs) started complaining of tummy ache last Saturday, vomitting commenced Sunday and continued until Wednesday morning, since then she has had the most awful diarrhoea, twice in her sleep (she has never even wet the bed prior to this). She has been eating a little since Wednesday but it just passes straight through, her lips are incredibly dry so I'm worried about dehydration. An hour ago Ds started vomiting too. 
Normally I wouldn't take them to the doctors, but it doesn't normally seem this severe or drag on so long. Obviously it's now the weekend and doctors is shut, dh thinks we should take them to out of hours tomorrow but I think they'll just say it's a bug, take them home to rest and give them fluids. I also have a 13 month old and am worried she'll get it next.
What would you do?
Thank you.