No one likes to be cold, but safety is our priority. When buckling in your child make sure to remove any heavy jackets, snowsuits or clothing that might prevent the harness from being properly adjusted. The child can however wear a thin jacket or fleece. Heavy items can compress in a crash, creating excess room in the harness that could allow your child to move and be injured.
After your child has been securely harnessed in and the harness is snug on the child, you can use a blanket or other item to keep them warm.