For the sense of sight we printed out a set of pictures and a mini set to go with them. I bought Lamb a magnifying glass and he matched the mini pictures with the ones that he could see clearly.
He loved this activity, applied himself with gusto and proceeded to inspect all kinds of things with his magnifying glass in the following days.
We also needed to have a discussion about the parts of the eye in an interesting way.
I chose colouring. Lamb is usually pretty against colouring. He loves to draw but just doesn't get into the whole 'within the lines' thing. He was quite interested in this though as we discussed the names of the parts of the eye, what kinds of eyes colours you could get and the corresponding eyebrow colour!
This lent itself to a discussion of counting in twos. He pointed out that eyes come in pairs and I went through the hard and soft counting to ten. He seemed to get it but we only did it the once. I'm not sure he's quite there yet....