Most experts suggest waiting until your little one reaches nine to twelve...
https://wiki-quicky.win/index.php/Do_Babies_Need_a_Helmet_in_a_Bike_Seat%3F_The_Truth_About_Safety_on_Two_Wheels
Most experts suggest waiting until your little one reaches nine to twelve months before bike riding. Your child needs strong neck muscles to support a helmet and withstand minor road bumps. Before you head out, confirm they sit up confidently on their own