Ask a child to read D&C 130:22. 

Teach that the Holy Ghost is a "personage of Spirit."  Explain that even though we can't see the Holy Ghost, we can recognize His influence. 

Display a basket of fruit and ask the children to identify the kind of tree that each fruit comes from. 
Have the child read Matthew 7:20.  Explain that we can identify a fruit tree by the fruit that hangs from its branches.  Have another child read Galatians 5:22. 
Tell the children that the Spirit is the Holy Ghost. 

Testify that we can know that we are feeling the Holy Ghost when we have these feelings. 
Have all of the children look up Galatians 5:22 and Mosiah 4:3. 
Invite the children to mark the words joy, peace, and faith and explain that these are also fruits of the Spirit.  Share a personal story of how the Holy Ghost has blessed your family. 

Sing, "The Holy Ghost" (CS, 105), and remind the children that joy, peace, and faith are fruits of the Holy Ghost.