We put a free choice feeder in with all litters at about 5 days of age! Clip needle teeth, notch ears, and give iron shots when they are 24 hours old. Dock tails, castrate, and give 2nd iron shot at 10 days old, wean showpigs, vaccinate for Flu/Circo/Myco/Ery, and worm at 28 days.
Pigs are extremely intelligent and they will play, if they know you generally have food or treats in your hands they will try to jump for the sometimes. But you have to be careful, there are some bloodlines out there that are known for being aggressive, and they will flat come after you any time your in the pen with them. Just like any other animal you have to curtail this behavior at a young age.