Denise,
gravity always pulls with pretty much the same force, at least over the heights you can reach in the classroom. But, gravity keeps something accelerating as it pulls, since it keeps pulling.
So, in the first second that an object falls, it speeds up from no speed, to 10 m/s. In the next second it speeds up another 10 m/s, so is now going 20 meters every second – so has now gone much further in the second second than the first.
You can see this on the ramp in this video:
https://www.pbslearningmedia.org/resource/nvmm-math-fallingbodies/galileos-falling-bodies/