You could wait, but then you risk those little mobile hands grabbing onto the hat and throwing it across the room followed by a bit of tantrum because they don’t want to wear a hat all of a sudden! By introducing babies to a hat when they’re still little blobs that don’t really move, you’re getting them used to having something on their heads, so by the time they’re able to be aware of things, they’ve already accepted a hat as daily wear – just as they have a nappy or clothes. This will save you the battle later on and start them on an important journey of sun safety - hopefully for life. Babies are also outdoors a lot in prams on walks or carriers - and a hat designed for both of these purposes will keep them protected from direct UV exposure. A legionnaire hat is also ideal for rear-facing car seats which often times don't have a lot of shade - a hat with a brim angled just so will keep the sun and glare out of baby's eyes.