I love sunflowers as they look so unpromising just the little stripey seed, then they don't grow very tall sometimes (like this year!) but then produce flower heads the size of plates and look absolutely beautiful! We had ten or so heads and the seeds needed to come out so set Faith at them with a pair of tweezers!! In the picture below you can see more of the tray showing the very simple set up! For the toddlers, I just put some heads in an empty deep tray and they sat for a long time picking them out by hand. Faith learned that she really couldn't cut corners and get two or three seeds at once with the tweezers..... she did have to be patient!!
As the toddlers emptied the seed heads I put them on one side as I thought that they might be interesting to print with. later on I couldn't find them until I looked at the nature table and one of my little ones had very carefully carried all the seed heads in and arranged them there. I was so touched at her thought and care.... she isn't quite two yet!