To start, glue two popsicle sticks together to form a cross. Yes the cross beam will be too big, but it's OK. (If I can quiet the neurotic perfectionist within so can you.) If you want to be fancy, you can paint or color the sticks green. I used a marker to color mine, but going forward, I will paint them or buy them pre-stained.
Next you'll need to take a piece of green construction paper and fold it in four. Cut out three individual hearts that are the same size.
Then you'll need to cut out the symbols for the Father, the Son and the Holy Spirit. I cut a smaller red heart for the Father, a yellow cross for the Son, and a white dove for the Holy Spirit. See the photo below to see how I made the dove by folding the paper in half and drawing one side of the dove. Once it's cut you'll have a dove.
Glue the three green hearts together to form a shamrock shape and attach the heart, cross and dove cut outs to the leaves (one symbol per leaf). Then glue the popsicle stick cross to the back of the shamrock.
On the top leaf of the reverse side of the shamrock I wrote: Father, Son and Holy Spirit: The Blessed Trinity
This craft is very simple to make and children who are old enough to use scissors will be able to cut out the big green hearts. Younger children will likely need help with cutting the symbols for the leaves. For my kindergarten religious education class I will glue the sticks together and cut out the symbols before hand to save time.