For the stem, I improvised with green felt using a pipe cleaner to give it support. Then we stuffed the ball and stem with batting.
The small ball is a great sewing project for kids as young as 5 years old. Use embroidery floss and an embroidery needle so if kids poke themselves, it's not so sharp.
The quality of the felt is important so we try to get 100% wool felt. It's a lot nicer to work with and can make these pumpkins everlasting. A Child's Dream Come True is a good source for natural 100% wool felt.