Also if they aren't ready for play-doh you can put play-doh inside of a balloon and then tie the balloon off so that they have a "stress ball" type of thing. Get to feel the play-doh without you worrying about them eating it or getting it into carpets, ect.
Also, you can try making discovery bottles:
http://kidsactivitiesblog.com/activities-for-one-year-olds/
The above link goes to a bunch of activities for one year olds but some of them would be appropriate for 7 month olds as well, especially discovery bottles which are explained on that site.