Make sure you have enough clothing, blankets, quilted bags, and other gear to keep your child warm.
Socks make excellent mittens and several layers of hats are recommended.
Use plenty of sunblock, wide-brimmed hats, and either goggles or sunglasses to protect their eyes. Devise a system for carrying your child that isn't too painful for the adult to manage. I used a Snugli front carrier until Piper was eight months old, then switched to a Gerry carrier. For our older daughter, we used a Gerry carrier fitted inside a Lowe Alpine Systems pack to take advantage of its superior suspension system. This may mean choosing tours without steep downhill sections or realizing that the person who carries the child may need to side-step down some portions of the trail.