We reviewed the plant kingdom (more in this post), then focused on the difference between monocots and dicots - they carefully removed the petals and counted them and examined the leaf shape trying to work out which group they belonged too.
We then moved onto pollination using wotsits and sweets. (the wotsits leave a cheesy residue on your fingers when touched - like the pollen sticking to insects when they brush past heading for the nectar/sweets)
and used some great sorting cards from Montessori Print Shop to learn about the different types of pollination.
There were a couple of short films on youtube and brainpop they watched before writing it all up.