Traveling Business Class between Atlanta and Hyderabad with Baby

Hi,

I am traveling between Atlanta and Hyderabad, India (ATL-LHR-HYD) with one biz seat and a lap child. How long are the BA bassinets or carry cots? I am trying to figure out if I need to reserve a carrycot of a reclining car seat.

Also, I am an Indian national transiting through UK within 24 hours from same terminal (T5). I have a valid US visa stamped in my passport. Do I still require an airside transit visa?

Any help is highly appreciated as I travel in 2 weeks.