In our house, we love science. My youngest will spend all day planting, weeding, watering and doing anything except school work. There are some fun science lessons with the garden. This is one fun thing we did just recently.
Take an empty 2 liter bottle and wash it out.
Cut the bottle in half (roughly - does not have to be exact or even neat)
Fill the bottom half about half way with dirt, put in your seeds (write on the bottle with sharpie what you are planting - I ALWAYS forget). Then take the top half and use it as a lid. The top will fit inside of the bottom.
Stick it in a sunny spot on the window sill
Within 2 weeks we were using a magnifying glass to view the roots. After the beans outgrew the bottle, we transplanted the plant into a pot outside and we are now eating snow peas every few days.