Every since my baby girl started vocalizing, her big bro has been baby talking. I thought it would pass but he's nearly three and he still does it. He clearly thinks it's adorable.

We have tried everything, ignoring, making him repeat things, talking about the perks of big boyhood.... and he STILL does it. (NOTE: According to his teacher, he doesn't do it at preschool.) He probably uses his baby voice and baby words more than he does his normal voice/words.

Anyone else have this issue with an older sib? What can I do?