Parallel and perpendicular are terms that your child will use their whole life time. Including it in daily conversation will help reinforce the meaning and allow them to naturally generalize these terms in multiple environments. Parallel is a surface or object is by your side and perpendicular is when the object is in front of you or behind you. We have a little song with hand motions we teach to the children that helps them remember which is which:
As they sing this song, they swing their arms back and forth by their sides during parallel and then turn 90 degrees to the left or right and either tap a wall or tap their arms crossed in front of them in Indian style for perpendicular.
Song: Parallel, Parallel, Perpendicular
By your side, by your side, in front (or back) of you.
Have fun exploring the world with your child!