A.E.
Hi T.-
I have a 26-month-old girl who has her moments of preferring Daddy, but not to any extreme. I sit back and try to enjoy the fact that she loves him and he is a participating Dad. I would guess it is a phase as well as what the other people said: Daddy is the plaything, the cold shoulder when with the grandparents.
I am a teacher and have worked with children for years as a ski instructor and teacher so I've observed many relationships between children and parents. In my own experience, too, I see that children react to very subtle reactions/behaviors/care-giving techniques that we each use. For example, my daughter prefers Daddy to change her diaper (YAY!) and I think it's because I have more of a reaction/facial expression that is negative. I try not to, but the smell can make me gag and I take steps to not smell it. So, she prefers Daddy. I did not do that on purpose and I DO try to not overreact.
So, my advice is be patient, it will probably pass. But also, observe ways that Daddy and grandparents connect. Maybe they give your child more independence to explore or wash his own face or help with chores. Compare your reaction to theirs ... falling, feeding, reading, changing diapers. I think we, as Mommies, are so in charge of the dressing, the feeding, the washing of the face, etc. and some of those things annoy them. Our reactions may feel more restrictive. So they react and want someone else when they are around. I agree with the other advice, to have Dad do more of the mundane chores.
Good luck T.. Just one phase on his road to full independence!! Hope this helps. A.