I have been recommending these for a long time for people. Instead of keep repeating the information, it's time to write up a mini review for them. Carpet and babies/toddlers do not mix well. How can you clean milk/food/drool/etc off carpet, three times a day? We have bamboo floors, which we love. However, little ones still prefer a softer area to play, and occasionally fall, on. Bring in the soft foam squares. They are colorful, they are soft, and they are not that expensive. Since they comes in squares, you can replace one if you need to. They also help define an area for the little ones. We use them to define a playarea for the kids within the loft. It forms a natural space. Others have also used them on balconies and roof decks.
Which brand to get? Forget the little one foot alphabet squares that you can buy from toy stores. They are not durable enough. Our first child torn corners off them. We found a online retailer that sell industrial strength mats. Those are designed for gyms and tradeshow floors. They are thicker, and much more durable. Note that they do NOT mate with the small versions. Try Soft Tiles. We have used ours for almost three years now, and they show very little wear and tear. At about $1.20 a square foot, it is worth it.