The parent and child. The parent knows he is to let the child feel safe and secure from harm, and is to do so during the child's whole life. When the chips are down, times become difficult through pain or fear the parent feels capable of helping the child through some kind of turbulence ahead.
In the second verse I feel that the tables are turned. The child has grown and the parent who is old or older is experiencing fear or sorts of insecurity. The child in turn does the same for the parent as the parent did for him/her and says, "hey papa (or mama) let me help. Lean on me for a change. "