What a Preschooler will Learn in this Peschool Biology Activity

What the pupils in their eyes look like

That pupils change size depending on how much light there is

What you will Need for this Preschool Biology Activity

A preschooler

Something to cover one eye (an eye patch or a scarf will work)

A mirror

What To Do

Step one: Have a preschooler cover one eye for a minute or two with the scarf or eye patch. Caution: Your preschooler's depth perception will be off, so don't let them run around or go up and down stairs.

Step two: Send them outside, or put them in a room with lots of light.

Step three: After a minute or two, uncover your preschooler's eye and let them look in a mirror. They should see their pupil dilate or change from large to small. This is a very fast change, so they will have to look quickly.

Variations on this Preschool Biology Activity

If your preschooler's having problems seeing the change in their own eye, cover your eye and try the experiment on yourself. Your preschooler may have an easier time seeing your eye change than theirs.

For Preschool Educators

Consider doing this experiment on yourself so preschoolers will notice the change in your eye rather than on themselves.

Hi! I'm Theresa Halvorsen, the preschool science and nature writer for Preschoolrock.com. I have twin boys and am blown away by their fascination with preschool science and how the world works around them. I am always looking for fun and simple science activities so preschoolers can learn about science and the natural world. Please contact me with any suggestions, ideas or questions you have about this site.

Helpful Tips for Parents

• Safety first: always supervise, taste-test nothing, wash hands after experiments. Model good safety habits — goggles, careful pouring, cleanup. Safety habits built in preschool persist.

• Always ask "What do you think will happen?" before running an experiment. Prediction is the core of scientific thinking, and preschoolers' predictions are always worth hearing.

• Repeat experiments multiple times. Reliability — the same result happening consistently — is a key scientific concept, and repetition gives preschoolers the proof they find satisfying.

• Science is everywhere: the kitchen, the garden, the bathroom, the driveway. Narrating daily life as science keeps curiosity active between formal experiments.

Frequently Asked Questions

My preschooler loses interest in the experiment before it's done. What do I do?

Most preschool attention spans support 5–15 minutes of structured science activity. Design experiments with quick visible results — the baking soda + vinegar reaction, the pepper + soap demonstration, the oobleck — rather than long-waiting experiments as a first experience. Save multi-day experiments (crystal growing, plant sprouting) for when the child has developed patience and the routine of checking daily has been established through previous successful experiments. End an experiment early rather than forcing continuation — a positive incomplete experience invites return more than a forced completion.

Should I explain the science behind experiments, or let children discover it?

Sequence matters enormously: always let children observe and wonder before explaining. "What do you notice?" and "Why do you think that happened?" should precede any explanation. If children ask why, give a simple, accurate answer — never give incorrect explanations to protect the mystery. After the child has observed and hypothesized, confirming or expanding their theory with correct information is appropriate and satisfying. Explaining first removes the inquiry that makes science learning durable.

Related reading: See also our science experiments at home and our nature walks guide for more ideas on this topic.

🎓 Skills Your Child Will Develop

• 💬 Science Vocabulary — Science introduces children to precise vocabulary — observe, predict, hypothesis, dissolve, absorb, transparent — that dramatically expands language range and supports the academic vocabulary children need in school.
• 🏗️ Engineering Thinking — Testing structures, materials, and designs to see what works develops engineering intuition — the practical understanding of forces, materials, and design that underlies all physical construction and problem solving.
• 📝 Recording & Documentation — Drawing what they observe, recording measurements, and noting results gives children their first experience of scientific documentation — and connects science to literacy and numeracy in an authentic context.
• 🔍 Observation Skills — Paying close attention to what happens during an experiment — noting colors, textures, movements, and changes — builds the observational precision that all scientific and analytical work requires.

Have you caught your preschooler blinking in the light or complaining about how bright it is after coming out a movie theatre? Or has your preschooler noticed that while star gazing, the longer they stay in the darkness, the more stars they can see? Would you like to explain how our eyes constantly adjust to darkness and light? After doing this easy experiment, preschoolers will understand how their pupils dilate so they can see in the dark.