Non-Kosher animals:[1]

One is to be careful not to show the newborn child any non-Kosher imagery, such as impure, Non-Kosher, animals.[2] Accordingly upon giving or purchasing a toy for a child, it should not be in the shape or figure of a non-Kosher animal, bird, fish etc, but is rather to be of only a pure species. Likewise, when the child gets older and is taught the alphabet using the figure of animals, he is to only be taught using pictures of pure species. The one exception to this is regarding pictures of figures that are written about in Tanach, in which the children may be shown the impure species described in Scripture in order to understand the material. Likewise, the above does not negate those synagogues which are accustomed to have paintings and inscriptions of various animal such as a lion and the like, being that the purpose of this is for a spiritual message.[3]

[1] See Kav Hayashar 2; Shevet Hamussar 24; Maagol Tov p. 56; Yeshuos Chochmah 33:11; Sefer Zechira; Sichos Kodesh Parshas Kedoshim 2:170; Hisvadyus 1984 20^th Marchesvan 37; Likkutei Sichos 25:309; Toras Menachem 5750 3:179 “It has been spoken a number of times on the need to be careful not to look at toys and pictures of non-Kosher  animals in order so children only see pure and holy things. This is so important that this adherence begins as soon as the child is born and comes out to the air the world, in which case we immediately hang around the child matters of holiness and purity. Furthermore, this adherence begins even before the child is born during the pregnancy. As it is known that the custom of women while they are pregnant to be very careful not to see impure items but rather only pure and holy items”; Sefer Shemiras Haguf Vihanefesh [Lerner] 237:2; See Megillah 28a; Shulchan Menachem 6:31; Shevach Habris 1:11

[2] The reason: As everything a child sees, even from a young age, is encrypted in his mind, and hence it is proper to abstain them from seeing anything which can ignite their Yetzer Hara when they are older. [see Kav Hayashar 2; Hisvadyus 1984 20^th Marchesvan 37]

[3] Likkutei Sichos 25:309