Goo is always fun. Just add water to the cornstarch until it is liquid, but forms a solid when you pick it up and roll it quickly in a ball (it will look solid/dry and then "melt" right away)...you may have to play with how much water to add to make it suitable for your 2.5 yr old. Its a really neat texture for kids to play with. You can also put some food coloring in for fun
