There is a common practice in the world that images of animals, such as dogs, cats, lions, and so on, are hung around the baby’s room. These are all impure animals.
We need to conduct ourselves differently. Instead of these images, our children should have a tzedakah box, a bencher, kriyas Shema, or alef beis and so on, so that when the child looks around, he sees things related to Torah.
Just as a mezuzah is placed in a double covering in order to avoid halachic problems, this should also be done with a bencher, kriyas Shema, and alef beis. They should be bright and colorful in order to be pleasing to a child.
First the child will glance at these kedusha objects, and then will come the hand motions. When the child begins to talk, he will take an interest in these things. He will then be explained that we have Torah, and that Torah is the greatest sechorah (merchandise), and when he grows up, he will be given this wonderful sechorah.
(Sichos Kodesh 5736, vol. 2, p. 170)
Seeing the face of a Tzaddik, even through a picture has a very positive impact on the neshama. One can be aroused in an exceptional way, and have all obstacles removed by envisioning a Rebbe. Speaking of the Frierdiker Rebbe, the Rebbe said that even those who never saw the Freidiker Rebbe in person can accomplish this by looking at a picture (Hisvaaduyos 5746 vol.4, p.311).
Babies spend a lot of their awake-time looking around and absorbing their environment. For this reason, making a baby mobile with either kedusha objects such as a Torah, pushka, Beis Hamikdash, Shir Hamaalos etc., or of pictures of the Rebbeim as depicted above can be a great way to make use of your baby's crib time. Just make sure that whatever it is you are displaying is visible from the angle the baby is looking from!