Snopes looked into this viral video of a very young kid (some people are saying she is 10 months old) drawing excellent cat cartoons. Snopes found several "small oddities" suggesting subterfuge: "For instance, the child turns its head around the 7-second mark after apparently hearing a noise, but the baby's hands continue to draw on the paper. And at the end of the video, the tail on the third character simply appears on the paper out-of-sync with the child's hand movements."
Snopes found other videos of the same child demonstrating remarkable talent:
If we presume that the Peppa Pig backpack in the background of the viral video belongs to this child (in other clips the child can be seen drawing Peppa Pig and wearing clothes featuring the cartoon character), it may be reasoned that this child was at least old enough to attend school and likely 4-5 years old. If that's the case, while this child's artistic abilities were impressive, such skills would be plausible.
The child in this video seems much younger that 4-5 years old. I'd say 2 years old is more likely.