As Otis (8 weeks) really enjoys batting his Gobbi mobile, today I put up his bell on a ribbon. I hung the bell from a ceiling hook in our lounge area. At the end of the ribbon there is some elastic so when he is ready to grasp the bell it has some give in it. We purchased the bell on a ribbon from Goose Designs.
His batting (and kicking) at the moment is accidental. He is only just making the connection that he is hitting the bell which is making the sound. Soon this will become intentional movement and he will know that he has control over his environment, he hits the bell and it make a noise. I believe this can be very empowering for a child to set out to do something (hit the bell) and then to actually achieve it (and cause it to ring). How rewarding!
The bell on a ribbon is like most mobiles, great for developing tracking and concentration but as this one is intended to be hit it is also great for developing coordination and learning about cause and effect.
Montessori emphasised being aware of the child's skill level and offering an environment that is supportive of the child but also challenges the child. This mobile is on the edge of Otis's skill level and is a definite challenge for him.