Adam had several reasons for getting Callie out of the house on her birthday. He genuinely believed she needed the alone time, especially since she spent her nights after Carter went to sleep keeping him entertained out of pity, but there was also something he needed to do that she couldn't be around for.
Carter had heard some people talking about Mother's Day the last time Callie took him grocery shopping with her and he remembered making a present for her at preschool last year and wanted to do it again.
The surprise would be ruined if she had to help make her own Mother's Day present. It needed to be done when she wasn't around but she never left Carter alone so he had to get creative.
He had wanted to spoil her on her birthday anyway. He figured it was the only time she would allow such a thing.
