Like the Shrink Panel, the Grow Panel is an Action Toy in Disney INFINITY. When walked upon, the character will enlarge, similar to the Goo Grower along with giving them a brief increase in power allowing them to pick up larger characters that were unable to previously and taking less damage, along with them getting a deeper pitch in voice. Cars and mounts such as horses are also effected by the panel.
The Grow Panel used to be known as the Grow Toy.
It's effect is very similar to the Super Mushroom from the Super Mario Bros. series (the same can be said of the Goo Grower), as it causes the character to grow in size, the deeper pitch in voice is likely similar to the deep pitched voice from the Super Smash Bros series when a character picks up the Super Mushroom in-game.