Sink or Float? | A Simple Toddler Science Experiment

Teach science through hands-on water play!

Toddlers are natural scientists — they love to drop, pour, splash, and test their world. This Sink or Float experiment is a perfect first introduction to science concepts like observation, prediction, and cause and effect.

It’s simple to set up, engaging for all ages, and full of learning disguised as fun. If your toddler loves this kind of play, you’ll find 25 more ideas in my guide to toddler sensory activities.

🎥 Watch the Experiment in Action

🧠 What Your Toddler Is Learning

• Cause and Effect – They begin to understand that actions have outcomes (e.g., “when I drop this, it floats!”)
• Observation Skills – Watching closely and noticing differences
• Early Language Development – Learning and using words like sink, float, heavy, light
• Categorizing & Sorting – Grouping items that float vs. sink

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🧺 What You’ll Need

• A plastic tub or bin filled halfway with water
• A towel or tray underneath (optional for spills)
• A variety of small household objects, such as:
  • Spoon
  • Block
  • Crayon
  • Pom-pom
  • Plastic lid
  • Rock
  • Apple slice
• Optional: a Sink/Float printable chart to mark observations

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🛠️ How to Set It Up

1. Fill your bin with water and set out your selected items.
2. Show your toddler one object at a time and ask:
   “Do you think it will sink or float?”
3. Let them drop the object in and observe together.
4. Sort the items into two groups: sink and float.

You can repeat this multiple times — toddlers love repetition, and each round builds deeper understanding.

💡 Tips to Extend the Play

• Try it with fall-themed items (leaves, mini pumpkins, acorns)
• Use clear containers for better visibility
• Let your toddler collect their own test items from around the house
• Add a dry erase board or chart to mark “guesses” and “results” for older toddlers

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📚 Part of Our October Curriculum

This activity is one of the 10 hands-on science experiments inside our Free October Curriculum for 2-Year-Olds, where we explore curiosity, color, reactions, and early STEM — without the Halloween theme.

👉 View the full October activity guide here