Over the last few weeks using a kit from a company called Insect Lore, we have been watching caterpillars metamorphasize into butterflies.
We did this once before when my eldest was little and thought we'd do it again for our youngest.
We got the kit from Amazon, although I'm sure it is also available elsewhere. This is the one we used https://www.amazon.co.uk/Insect-Lore-10416-Butterfly-Garden/dp/B00000ISC5/ref=sr_1_1?ie=UTF8&qid=1468786794&sr=8-1&keywords=insect+lore+butterfly .
The kit comes with a butterfly habitat, feeding pipette and a voucher. The voucher you send off to the Insect Lore company and they send you a small tub with 5 caterpillars in them. They are really tiny when they arrive but in the next week grow to 10 times their original size.
For those that are not keen on creepy crawlies there is no need to handle the caterpillars as the tub has air holes at the top and contains a brown substance on the bottom which is the caterpillars food.
You leave the caterpillars in the tub until they turn into chrysalises which they start doing by hanging from the lid in a j shape. Once they have hardened over a couple of days into the chrysalises you take the lid to which they are attached and put this in the butterfly habitat.
About one week later your butterflies should start emerging. There is something kind of magical about the whole process. The butterflies climb onto the side of the net and you can see them testing out thier wings.
After a couple of days you release the butterflies on a warm day in your garden. The boys really enjoyed this and although they were sad to see them go they were excited that the butterflies were going to lay eggs and start the life cycle all over again. We had one very placid butterfly which sat on James's hand for a while before leaving which was really sweet.
I would highly recommend this activity for children and it is something they'll always remember and a lot more intresting that learning about life cycles from a book !