Our church purchased some interlocking rubber mats made by Step2 to go under the climbing mats in the toddler nursery. We wanted something safe, but fun and these mats seemed to fit the bill.
These mats have tongues and grooves just like puzzle pieces and are very easy to put together. They are slightly textured so little feet have traction. They are made of 3/4" thick foam, which makes them very soft and a much safer surface than the carpeted floor. They come in four bright colors.
These are sold in packages of four, and the tiles are 24 inches square (so, each package results in a 4 x 4 foot area being covered). You will have to purchase multiple packs in order to cover a big surface, so it has the potential to get pricey.
One of the reasons I love these mats so much is that they are very easy to clean and disinfect which is great when you have kids around.
One thing I did not like about these mats is they smell when they are initially taken out of the package. It takes a while for the rubbery smell to dissipate, but once it does they have no smell at all.
I would recommend these floor tiles to anyone wishing to cover their floor with a surface that is kid-friendly, whether it be at a church, school, or in your own basement.