This often involves snuggling in bed feeding the baby whilst the toddler watches some cartoons or plays games on the tablet.
Most of the time he is not too concerned about her but he does look for her in the mornings and sometimes he holds her hand when he's watching cartoons which is sweet.
Also he gets protective when other kids show an interest in her. At a mummy group a little girl kept fussing over her and trying to put her dummy in and he came over and said, "no! My sitter!" So hopefully he will play the protective older brother and look out for her in the playground and scare away any potential boyfriends.