As long as you can return the item, you can get a price adjustment. Just return the item and buy it back.
But Toys R Us raises the prices on a lot of the most popular toys, like
LEGO sets, by about 10-20% right before Christmas. So even if something is on "sale" now, it might have been cheaper when you bought it.
The LEGO City 25% off sale this week is a joke, because they raised prices on LEGO City sets 20-30% last week!
So, for example, the Helicopter Transport set was $40, was raised to $50 a few days ago, and is now $37.50 at 25% off.