An activity that most children enjoy when out in nature is collecting sticks. Sticks can be great for imaginary play, for example being knights or pirates. But they can also be a great tool for teaching about lengths and widths.
We do an activity where we go to a local park or woods, collect about 10 fallen twigs. Then once we are back home we use chalk and write on the ground ‘long’ and ‘short’, and ‘Thick’ and ‘Thin’. Then we get our son to sort the sticks to these measurements. Measuring the length first then go onto arrange them in order of their width.
You could also collect fallen leaves and measure them into size order using ‘small’ and ‘big’.
I find it much easier to teach my three year old son colours, shapes, sizes etc when out in nature. If I try to teach him whilst inside at home he shows no interest. If you struggle to teach your little one at home why not go out and test their knowledge in a local park.