Wait until your little one holds their head steady and sits up independently...

https://wiki-quicky.win/index.php/Do_Babies_Need_a_Helmet_in_a_Bike_Seat%3F_The_Truth_About_Safety_on_Two_Wheels

Wait until your little one holds their head steady and sits up independently before you start biking. Most families look for these developmental milestones around nine to twelve months. Always ensure a tiny helmet fits snugly before your first ride