The personalisation editor is designed to configure one customisation per product. Even so, keep in mind that in the case of Stikets Packs, you get an automatic 8€ off for each additional Pack you purchase. The discount is instantly applied when adding any additional Pack to your shopping cart.
If you have several children and want to use the same label set for all of them, you could
include only the surnames on the labels. If you do this, a good option is to also customise the product with a combination of colours and assign each colour to a child so as not to mix their things.