The head is considered the most sacred part of the body. Don't pat children, don't reach over someone's head, and never tousle hair playfully.
Even with affectionate intent, head-touching makes people uncomfortable. This applies to babies in strollers too — admire from a respectful distance.
Feet are the opposite — the lowest, dirtiest part of the body. Don't point your feet at people, religious icons, or step over someone seated on the floor.