My son is almost 5 months old and has been sleeping in his Nap Nanny since he was 1 month old!
He absolutely loves it! It does not seem natural to sleep completely flat so the positioning of the Nap Nanny (which is similar to a car seat) is perfect. There is plenty of room to grow and a seat belt to keep baby safe! Invest in one and sweet dreams to all.
I highly recommend this product!