First of all, it is necessary to register as an FOP (group II or III). In addition, I inform you that the FOP can be opened in the "ACTION" application in a few minutes.
According to the requirements of the Tax Code of Ukraine, single tax payers cannot sell art objects, which include: paintings, drawings, pastels, watercolors, original prints (prints, lithographs), sculptures, figurines, etc.
Therefore, if the bank or accompanying documents for the goods (bill of lading, invoices, receipts, etc.) will indicate exactly the names of the goods (classified as works of art), you will not be able to be a single tax payer. Also, just avoid names in the documents that may indicate that you are selling works of art. Replace them with other, more neutral names.
As for KVEDs, there are no separate ones for foreign economic activity. You should have a list of KVEDs that corresponds exactly to your activity (a list of goods or services that you sell).
In addition, in order to avoid possible conflicts, it is necessary to conclude a contract with the person who drew the coloring pages for you, which, among other things, will state that you have the right to sell them.