We travelled to Las Vegas for the NHL awards in June. We stayed at the Wynn with my two kids (2.5 and 10mo at the time). We booked a room for two adults because we were not sure if the kids were going to come. Upon arrival, not only did they NOT charge us extra for the two kids, they offered a crib and a fridge at no charge.
One not so great thing about the hotel is they close the lower floors when they are not busy. So we had to stay on the 14th floor because we couldn't get anything lower. Not ideal for someone who doesn't like heights.