Praise be to Allah (The Glorified and Exalted).
1) Passing religious rulings should be done by individuals that have studied religion within a school and possess insight and wisdom. In some cases, it is not as simple as reading a verse from the Qur'an or a hadith.
2)
This person's intention in creating a cartoon for children, teaching Islamic manners, and promoting things such as working hard, team work, resisting evil, etc in cartoon characters, is commendable.
Muslims are in need of media such as films, cartoons for children, and video games with Islamic characters, culture, religious teachings, being promoted and taught. Or else all you have is what exists in modern times, in which non-Muslims have completely filled the world with their films, cartoons, comics, and video games that are widely available. This leads to the spread of fornication from lewd images, and a destruction of Islamic teachings and lifestyle, being washed out by non-Muslim lifestyles and manners, leading to a declination in religiosity among Muslims.
These people telling you to not create a cartoon, do not possess proper understanding. They do not take the time to reflect that Saudi scholars have permitted the spread of non-Muslim cartoons within their own territory. That is sure to corrupt the minds of Muslim children. There is a concession in these things such as drawing images, that is permissible for the learning and entertainment of children. Such as creating images of humans and animals in toys and allowing children to play with them. This is mentioned in the following hadith:
Narrated Aisha (may Allah be pleased with her), Ummul Mu'minin:
When the Apostle of Allah (peace and blessings of Allah be upon him) arrived after the expedition to Tabuk or Khaybar...He asked, "What is this (after removing a curtain within his home)?" She (Aisha) replied, "My dolls." Among them he saw a horse with wings made of rags, and asked: "What is this I see among them?" She replied, "A horse." He asked, "What is this that it has on it?" She replied, "Two wings." He asked, "A horse with two wings?" She replied, "Have you not heard that Solomon had horses with wings?" She said, Thereupon the Apostle of Allah (peace and blessings of Allah be upon him) laughed so heartily that I could see his molar teeth. [Dawud, Muslim]
A cartoon should be created. It may be used to promote Islamic teachings in various ways: For example, characters from different races may be present, and working together as a team, thereby teaching Muslim children to resist racist feelings and feel a union among themselves. There may be characters, for example, that are very good with technology and computers, thereby inspiring some Muslim children to get involved in such studies as they mature in age. There are various themes that could be played to teach different lessons. Of course the cartoon must be made for entertainment, because this is what draws the attention of children. Islamic teachings are presented in a more covert manner. There may be also images, such as the Kabah presented, and Arabic dress and caligraphy presented, etc to make the children proud of their Islamic traditions and lifestyle, so they may adhere to them. Such a cartoon will have great hopes of being accepted in many Islamic nations, as they are in need of such media, but may lack individual companies producing such forms of media, either due to lack of technical abilities or finances.
The same is to be said about creating films, video games, comics, and clothing attire. If Muslims do not get involved in such things, then the same will happen to them as what occurred to the christians in the west. They remained remote for a long time. The result, their hollywood films and television programming was created by individuals that are largely atheist liberals, thereby turning religion into a mockery and promoting their own heathen lifestyles and approach to life, which has now become prominent in those lands. Those people that say Muslims should simply focus on reading their children the Qur'an for entertainment, are ignorant indeed, they have no knowledge of human nature and how to govern a population. Their result will become like the puritan christians of america. Their later descendants became some of the most liberal minded people in all of the america and abandoned their religion. Life must be balanced, especially for children. A grown man with a high degree of intelligence and wisdom is not in need of watching cartoons, films, or sports, or playing video games. However, the knowledgeable man is aware that these things were created to amuse and preoccupy children and the "common man," which is the overwhelming majority of the population and must be taken into account.
And Allah (The Glorified and Exalted) Knows Best and may the peace and blessings be upon His Final Messenger.