The first stage is to do all the handprints by painting their hands and having them press their hands onto a piece of construction paper. Use a paintbrush to brush acrylic paint onto your child's hand and help them press down. Be careful to get some pressure on the palm and each finger for the best impression.
After the handprint paint has dried completely, cut it out and assemble the pot and cactus.
For the final detail, let children glue on their own flowers using one dot of kids glue per paper flower. You could also use tissue paper to make mini flowers.
Write on the back to make it a card, or poke a hole to turn it into a cute gift tag.
Notes
You could also trace their handprints onto green paper and decorate with markers, crayons, and stickers if you don't have paint.