Mega Bloks are fab for little ones, and this Mega Bloks ABC Learning Train is a cracking buy at Amazon right now. It's usually around £10, but it's dropped to only £7.49, with free delivery for Prime customers.
This set includes an easy-to-build train with 3 rolling wheelbases, and lots of building blocks to make your own train. Included are 57 big building blocks and special pieces, featuring all the letters of the alphabet so kids can learn as they play.
My youngest had this train when he was little and it was a big hit. He loved building with the blocks and wheeling the train around, and the educational aspect was a bonus!
There's free delivery with Amazon Prime, or on orders of £20 or more if you're not a Prime customer.