I think that it is necessary to OFFER scientific cartoons. As a child, I myself was very interested in watching many of them. The same "Smeshariki" are great, I still love them. But if you show ONLY scientific cartoons, you will only enter into a BIG conflict with the child, he will still watch entertaining cartoons and what he likes secretly from you, or are you still planning to deprive him of the Internet?) In short, the idea is unpromising ) A person's desire for freedom is a natural need, and in children it is even more pronounced)
I do not think that scientific programs and lectures will be of interest to a child. And interest is the most important thing in the study of any direction of science. It will be much more useful if the child buys educational games, cool constructors. My mother in childhood, if she could not answer a bunch of questions about the universe, always bought expensive editions of colorful illustrated books, some cost about 10,000 rubles. (This was almost half of the family's monthly earnings.) Thanks to them, at preschool age, I knew the name of the stars, looked for them in the sky at the dacha in the summer, knew the structure and composition of the nuclei of all the planets of the solar system, understood well where different countries were, knew their population, currencies. And much much more.
Recently I watched the cartoon with smeshariki "PinCode", so cool it is made, very pleased with the presentation of complex information, for example, about the properties of photons, the structure of digital cameras and their history, the human immune system. It is easy and understandable for a child, and most importantly - interesting.
The task of a parent, in spite of the education system and other factors that spoil the young mind, is always to maintain in the child a spark of curiosity and interest in comprehending and understanding the world, and not to be fenced off by scientific transmissions and think that this is intellectual education.
Firstly, educational programs must be adapted to the age of the child, otherwise the information will be perceived as street noise at best.
Information needs to be "processed" to be put into practice. Even the multiplication table is useless if you do not train by examples in life.
As a conclusion: you will not bring absolute benefit to the child, because scientific films are not a panacea, and on the other hand, by excluding cartoons from the life of a child, you deprive his rich impressions, aesthetic pleasure and cultural ties with peers. Cartoons aren't always just entertainment; and yes, a person should be entertained.
This is not a bad idea in itself. Serious harm can only be done by the crude embodiment of your theory. Experiments on a person never ended well for him.