Yeah - the last thing you want to do when doing introductions is already feel stressed by the magnitude of something like a holiday, which with kids, is already stressful enough as it is! There are just too many variables that would require controlling, which doesn't really sound particularly relaxing for anybody.
That said, the kids are younger - doing something similar with an older child (say, 5-6) would probably provoke more disobedience or issues as they tend to be a bit more compliant to authority at that age (as in, they look to their parents for safety, oppose to an older child saying "Mummy/Daddy made me do this" which invites blame). I'd definitely suggest a day trip out - being mindful of individual kids schedules (naps, if any, or behaviour when hungry/tired/overwhelmed).
I don't have kids, so when I started to get to know DSS I wasn't really aware of his individual quirks - DP was fantastic in really explaining his particular behavioural patterns when over stimulated, overtired, hungry, bored and ill. Maybe worth before you do your "big day out" you and DP sitting down, and advising each other what to look out for? Like "Oh, when Sarah is getting hungry, she starts grizzling but also denies being hungry" or "Joseph gets hyperactive when he needs to eat, like final burst of adrenaline" - I'd say this is especially true if any of your children have additional needs 
Good luck 