He is 3. Relax. Kids regress for all sorts of reasons. Ypur child is enjoying the attention he gets. Kids catch on quick that babies are adorable and acting like one gets the grandparents attention.

Just nip it in the bud when they leave. Harry, I know you can sit by yourself/ feed yourself.

My kid is almost 11 and his behavior is never fun after spending time with grandma. It's always been this way. I've tried letting my mom know that it's hard on him (and us!) every time he comes home or when she leaves if she is visiting us. Didn't help.

Don't have any advice, just wanted to say that you're not alone!

My DS has terrible behavior (not regression, just wild and out of control when he is generally a well behaved kid) when his grandparents visit and then when they leave. They do not say no to him which is annoying for me (and DH). But, they adore him and want to spoil him and I try to see that as okay coming from grandparents.

At some point your DS will probably tell grandma that he is not a baby, and that will be that though they will likely spoil him and cause some other temporary behavior changes on their visits at that point.

I just cradled my three year old like an infant this morning. I think he's going to be fine.