Project Learning Tree has an awesome Nature Journaling Resource with an introduction to Nature Journaling on page 8.

For the first journaling activity, write some Poet-tree! Take your children outdoors to observe a variety of trees and then encourage them to write a poem about why trees and forests are valued.

This activity is adapted from page 39 of the Back to Nature Network's Into Nature Teaching Guide. 

Give your child a cup and go out to a natural area to make a nature sundae or beverage by collecting nature items from the ground e.g. plants, soil, etc.

Ask your child to describe why their sundae is the best sundae in the world using  various adjectives that appeal to each of the senses.

Find 3 different trees to measure.

Use a string to measure around the tree,
cut the string. Lay down the string.
Which tree had the biggest tree trunk?

Challenge: Use a ruler to measure the
length of the string and record the
measurement of each tree. Which tree
had the largest trunk size
(circumference)?

Find six sticks that are around the same length.

Ask your child to keep one stick whole, break one stick in half,break one stick into fourths, break one stick into thirds,break one stick into eighths and break one stick into sixths.

Prompt your child to line up your matching fraction pieces in lines next to your whole, putting your fractions in order from largest to smallest.