We have the circus train multi-car train pack but we actually got it as part of Joe's first train set. I bought the circular circus train set that came with the circus cars and an engine and a circular wooden track. apparently this set is now retired, but you can still get the circular conductor set or seasons on Sodor set.

The circus train pack consists of three carrier cars. One green, one red, one yellow. It also comes with a zebra, a tiger, an elephant, and a giraffe. Unfortunately these animals are just wooden cut cut outs with the animal pictures painted on the sides. My son has more fun hauling around things like his small plastic spiders and bugs in these cars.

The plastic Thomas sets, called Thomas motorized road and rail, seemed to me to be room for the youngest kids who like Thomas. Turn on is easy, just a flip of the switch. My preschooler no longer plays with the plastic sets, they seem a little simplistic for him now.

My son has recently become interested in a new aspect of toy trains. It used to be that he would only play with trains by himself or kind of next to other kids. These days he likes to watch other kids play with trains on videos -- there is a Baby Genius video that has kids playing with thomas trains during one of the songs and he asks to watch it over and over again. There is a series called I Love Toy Trains available at netflix or at amazon or allaboardtoys - I got it just a few days ago and my boy is very interested in it.

Because the Thomas trains are the best train sets for kids (IMO), they're expensive. I have considered the less expensive Thomas compatible sets before, like Brio tables or the Brio roundhouse, but I have never bought. The train tables are shorter, a little smaller, and less sturdy -- the Round House has no turntable in front and the doors are harder for little hands open.

Thomas trains and sets come in wood, plastic, and metal trains. None of the train sets are really set up to be played with the other ones - for example, metal trains will not fit on wooden track. All of these toys are built to last- I have never had one break.