When the length of the sprout is ten to twelve inches long you will need to dig a small portion of the sprout out of the potato. Plant the slip as soon as you plan to cut it. It won't take long for the slip to adapt to the soil and take off. Last year I had vines as long as 15ft. and they were everywhere in the garden. The vines make a great ground cover or cover crop to keep down weeds and keep the soil shaded.
I think this would be a great project for kids to do.
Have a great day!!