I started heavily signing from 6 months up... although I signed earlier I only concentrated on 5 signs up to then... milk, more, all done, light, and potty ... and then shortly after eat and drink ... the different foods as I introduced them got signs.
My 7 month old loves the math. I do recommend the math at this age... according to Doman the math is easier to do at this stage then reading.
I do a music appreciation with my 7 month old
As for crafts I recently did yogurt painting with finger paint in his high chair with food coloring explaining how to make different colors
Bubble blowing is a BIG hit
Scarf playing and dancing (lots of spinning) is a fun activity.
I do find that this is a stage where they get bored a little easier... they want to be more active but dont have the capability... they cant sit too long because they want to do everything and touch everything and want to be included in everything...
We do a lot of poems as I switch him from room to room with me... Im always talking to my kids ( I have finger rhymes and poem books in every room of the house and often will print a song off the internet and post it to my bathroom mirror and sing it while im getting ready
I do shape tracing as an activity and trace different shapes with their fingers... cirlces on glasses, squares on tupperware.
Hope that helps!!