My daughter stopped napping around 20 months, even though she was in daycare full-time.
It started with her resisting naps at home on the weekends - we'd have to put her in the stroller and walk a minimum of 45 minutes, then transfer her to her bed. Eventually, we decided it wasn't worth it, since she'd only nap for 45 minutes anyway, and then would be up until midnight. (She never slept in the car, so that wasn't an option either.)
By 2 years, she'd pretty much stopped napping altogether - even at daycare. She went to bed earlier and slept 12 hours (8 till 8). If she got a little tired during the day, we'd simply have 'quiet time' by reading to her in her room. Don't get me wrong, some days it was hard and we really wanted her to nap, but she would just fight it. Other days, we'd do everything we could to keep her awake and stretch her out towards the end of the day (if she napped that late, we'd have trouble with bedtime later than 12 am). She's now almost 3.5 years old and the same routine continues.
As mentioned, as long as they get the number of hours of sleep they need and they don't get (too) cranky, then I think you should follow their lead and not force the nap issue, or it becomes a power struggle.
