A basket of balls and a slide or a simple board are all you need for this first activity! This is one we've done since well before he was walking, as our little daredevil mountain goat was climbing his stand-alone slide ladder and going down the slide head first before the time he was about 9 mos old! He was also a huge fan of balls at the time, so this game/little science experiment developed naturally. We've talked about the concepts of "up" and "down" and Tyler often experiments on his own by putting other objects from around the house down the slide to see what they will do. Using both heavy/light and big/small balls for this activity provide additional learning opportunities.
When he was younger I put the end of the slide into a kiddie pool so the balls didn't roll away as far and it was easier to retrieve them himself and roll them down again. I've found that putting a box or large container at the end to stop the balls is still fun for him now at 20 mos old.
As Ty gets older, we'll likely play a cooperaion/sharing game where we take turns being at the bottom of the slide to catch the ball, walking it to the person rolling, and returning to the bottom of the slide to catch, as well as moving further and further away from the bottom of the slide to catch.
Last month we took the idea of rolling balls down the slide a bit further, adding bowling pins for what we call "slide bowling". He gets a big kick of out this!
We also found a way to work on color recognition in a fun way! This large, soft die is from a game my parents purchased for Ty from Discovery Toys that he's not quite ready for yet. Tyler rolls or bounces the die down the slide, then we look at whatever color faces up and name it. Sometimes I look for something in the room or on our clothing to match the color to as well, then toss the die back up to him to start again.
Rcently Tyler has become quite entranced with cars, so look-out for a post on car ramps soon...as soon as I decide how to build what I've been imagining...