ShiBui gave you good advice. Follow general care as for Japanese white pine. If you are in the USA or Canada, I suspect that they are Pinus strobus, American or Eastern white pine. They could also be Pinus flexilis, Limber pine. They could also be Japanese white pine, or even Korean nut pine. Depending on how creative your source was obtaining these seedlings. Why don't you ask them? . An identity would be helpful, as there are subtle differences between all the 5 needle pine species.
But if you follow general techniques for Japanese white pine you will do no harm.