Hi. Ds is 7 months weighs just over 9kg has brilliant head control but can't sit unaided for long. His feet are scrunched up in his rear facing car seat and his head is at the top. We literally have to squeeze him into his seat at the mo. I know he's heavy enough to go into next seat but should we wait untill he can sit unaided for longer?? Would appreciate your wisdom on this folks.