I guess this depends this depends on the 3 year old's interest level. I received my first train at age 3 years 1 month in 1946, a Lionel 726 Berkshire set with several cars including a log dumping car, box car, crane car and caboose with a searchlight. Within a year i had learned to disassemble and reassemble the engine all by myself.
When my eldest daughter was 2 years 3 months she had already shown an interest in trains; loved riding the cable cars in San Fransisco and we couldn't get her past a Spencer's Gifts window in the malls where a train on display did back flips. Well after Santa spent several hours the morning of Christmas Eve in the basement trying to make the "back flipping train" work properly, he left for one of the discount stores (K-Mart?) and spent $40 of his last $50 on an entry level Lionel (MPC) set pulled by a NW-2 switcher. Turned out to be a wise purchase for her and later on for me too.
So my answer is, it depends on the child. But while not going way above what you think is their ability level don't be afraid to challenge them; kids are a lot smarter than we might think, and they go for the new command controlled stuff like a bear goes for honey.
jackson
