Just look at that smile! On Monday, Reese Witherspoon dropped a cuteness overload on Instagram, sharing an adorable picture of a frame-worthy moment with her youngest son, Tennessee. "Sweet lil walks with this sweet lil guy #Vacationmood," she wrote in the caption. The little guy, who will turn 3 years old on Sept. 27, lit up with a smile and struck a cute pose as Reese held his hand. While Reese is a familiar face on Instagram — she loves to treat fans to an inside peek of her family life — pictures of little Tennessee are rare. This new snap shows just how much he's grown since the duo's special moment last July.