Italiana, you sound very certain but I think that you are slightly misguided.
I would agree that most children aged 2 do actually need an afternoon sleep. However, some clearly do not. We have the exact problem that familiessharegerms talks about - getting into a vicious cycle of nap -late bedtime - tired in am - nap - late bedtime, hideously screamy etc etc etc.
There is commonly, IME, a period where the nap is on its way out that is tricky to manage. Some day sleep messes up bedtime, but no day sleep makes the child a bit grumpy and tired in the day.
Surely, what nannies and childminders should be doing is working with the parents to meet the needs of the individual child, not trying to impose a one-size-fits-all policy on sleep on all their charges? It can be tempting to think that all children are like the children you've known to date (or like the books say they should be) but in reality there is a wide spectrum of normal (not suggesting that you're doing this OP, by the way!).
On the issue of waking a child, really, you shouldn't feel bad about this. If I get a rare chance for an afternoon nap, then I have to set an alarm to ensure I don't sleep longer than an hour or so otherwise I'm up until 2 a.m. and therein starts a horrible cycle of late to bed, overtired ... Some children are the same.
I think the truth of the matter is that in family life, everyone's needs should be met as far as possible. Obviously, knowingly depriving a child of needed sleep is cruel, as is prodding them awake when they are so tired they are falling asleep in their food. But there is nothing wrong with avoiding the things that always send you child to sleep (cars, pram rides) if you know a sleep's not in their best interests in the long term.