In 2005, it introduced the first sets in their Duplo "Thomas and Friends" series. Five sets were made, featuring James, Thomas (in 2 sets), Toby, and Percy. Each year since, in line with usual LEGO practice, new sets have been released featuring different scenes and characters. The range ran until 2010, when it was discontinued because HiT Entertainment signed a deal with Mega Bloks to make construction sets based on Thomas.
Duplo is designed for very young children, so the sets have relatively few pieces to assemble.
- James at Knapford Station
- Thomas Load & Carry Set
- Toby at Wellsworth Station
- Percy at the Water Tower
- Thomas Bridge & Tunnel Set
- Percy at the Sheds
- Thomas Starter Set
- The Express Coach is painted maroon instead of red. The shade of cream used is also slightly different to the one used on the coaches in the show.
- Toby has no sideplates on his model and his wheels are grey.
- James' wheels are grey, when they should be black.
- James, Thomas, and Percy all have the same design, each with small modifications to make them look more like their television series counterparts.
- A LEGO model of Thomas with LEGO System bricks was featured in TM Books and Video's home video, "I Love Toy Trains Part 7".
- The "Thomas Starter Set" was briefly seen at the end of the animated video "The LEGO Story".
- The platform that Sir Topham Hatt stands on at the end of the first season episode Thomas' Christmas Party is made out of LEGO bricks, and it was also the scene of the second season episode Break Van is made out of LEGO bricks near the Water Tower at Wellsworth where James and Douglas leave the station. However, it is made of the more traditional, smaller bricks, known as "System" bricks, as opposed to the larger, toddler-aimed Duplo bricks the Thomas range (which was first produced over 20 years after the episode aired) is made from.
- The Knapford Station roof looks similar to the Kirk Ronan Station's roof.