First iron your fabric to get as many wrinkles out as you can, this will make it easier when painting on it. 

Start with the grass and just make small strokes over and over again, lighter and darker with paint at the bottom of  the apron. Make the stems to your flowers for the same color as your grass.

Next you will need to paint your child's hand and press it down onto the stem of flower. Repeat the step with a different color for each flower. If the hand prints come out too light you can fill them in with paint after.

Next you're going to paint your child's feet and place them down to make butterfly. Making sure to leave a space between the footprints for the body of the butterfly.

Using a thin paintbrush paint the body of the butterfly and make little dashes underneath for the flying line.

Above the flowers hand paint a yellow oval and black  lines and wings to make a bee. Use black paint to make dashes for the flying lines behind the bee.

Allow the paint to dry fully before moving.