Mattel Inc. has completed its $680 million acquisition of HIT Entertainment, which owns the “Thomas & Friends” franchise. The seller is a consortium of funds led by Apax Partners.

HIT Entertainment is a London independent children’s entertainment producer and rights-owner whose characters include Thomas the Tank Engine, Bob the Builder and Angelina Ballerina. Mattel on Tuesday night said that the acquisition, first announced in October, should bolster its sagging Fisher-Price unit, which makes products for pre-schoolers.

The El Segundo toymaker reported Tuesday that Fisher-Price sales fell 10 percent in the fourth quarter even as its Barbie, Hot Wheels and other established brands grew between 4 percent to 6 percent.

HIT is Mattel’s biggest acquisition in about a decade. Created more than 65 years ago, the Thomas & Friends franchise is considered the world’s top licensed preschool toy property.

“This is indeed a momentous day for Mattel, especially Fisher-Price,” said Fisher-Price Executive Vice President David Allmark in a statement. “I am very excited about the prospects ahead for the collective Fisher-Price and HIT Entertainment brand portfolio. Each business has complementary capabilities – the combination of which presents a dynamic future.”

Mattel shares were up 29 cents, or less than 1 percent, to $31.29 in midday trading on the Nasdaq.