One Finnish study and one German study found that vegan children were deficient in Vitamin A. This claim was propagated by Joseph Everett of the "What I've Learned" channel.
If you read the papers, the Finnish study states that "The linear model for vitamin A status considering inflammatory status did not classify any vegans as vitamin A deficient, but showed significantly lower status for vegans than omnivores" and "Our results indicate, however, that the vitamin D and A statuses of children following a vegan diet require special attention". Again, this is "be careful to plan your vegan diet appropriately".
In Table 3 of the German study, Vitamin A was found to be 1.8 ± 0.3 and 2.1 ± 0.5 for vegans and omnis respectively. What's funny is integrating a normal distribution between the reference interval limits of 1.46 and 2.84 with μ and σ with the respective values for the two groups, you actually get 87% of vegans and 83% of omnivores within the reference range. Oops. Now, it should be stated that this is probably not statistically significant. But in general, don't cite evidence that proves you wrong.