I just heard on the radio news driving to work that the UK is having some kind of Big Bad Weather Warning. People being warned to stay inside blah blah? (I’m in West Oz, so obviously a very slow news day, mind you.)
Yet another example of someone who doesn't even live here bashing the UK. FYI we have a dusting of snow - actually it's really pretty. The roads are clear. Scotland is having a lot of snow today, but the bit I'm in is having a beautiful, sunny, crisp day. I just walked my kids to school. Yes, you need to wear a coat, hat, scarf and gloves (gasp! imagine that!), but if you're properly dressed it's a lovely day to be outside, if only because the subzero temps have frozen the mud 
I know one family who moved back to England for 18 months - lasted one winter and came back, the kids (age between 5 and 10) were sick all the time and hated the cold.
And yes, if you move back here for one winter your kids WILL get sick all the time. It's because the native stew of viruses is different wherever you go, so if you move to the far side of the world you're going to encounter ones that you don't have immunity to. It gets better after a couple of years. When we moved back here from the US everyone apart from me (a native Brit), got colds and coughs, etc, because they didn't have any immunity yet. My advice - come anyway, get a flu vaccine, avoid sick people if you can, and accept that if you have a bad winter for illness it doesn't mean that every winter will be like that - it's just a phase in your adjustment to a new environment.