Any good internet source for learning Chinese for preschooler?

You can try this app! It is an interactive English-Chinese picture dictionary with audio. The vocabulary themes are animals, transportation, food, face & body, farm, toys, nature, clothes, and house. There is a quiz section for review. https://itunes.apple.com/us/app/lingupinguin-free-english/id420663681?mt=8

I know your feeling. I bought this for my kid, we learn from each other, i think the important part is interacting with your kid. here you go, https://www.lazada.sg/products/creative-knowledge-ar-magic-chinese-i304768171-s541126177.html?spm=a2o42.searchlist.list.14.10cf7745oCdv0u&search=1

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I would suggest Roseta Stone