One year old playing

Harley

My little boy just turned one on the 16th of this month and I'm due with his baby brother in November whenever I sit in the floor and try to play with him like rolling a ball or just doing different things he shows no interest and wants to be by himself but whenever his dad is not working all he wants to do is play with his dad.. I'm just wondering if it has to do with me being pregnant or if it's because I'm always with him and his dad is not?