Wait until your baby sits unsupported for ten minutes, usually around 9-12...

https://super-wiki.win/index.php/What_Age_Can_a_Baby_Ride_in_a_Front_Cargo_Box_with_a_Seat%3F

Wait until your baby sits unsupported for ten minutes, usually around 9-12 months. Front seats keep them close, rear seats suit active toddlers, and trailers offer the most stability. Ensure they hold their head up well. You’ve got this!