Just do it. No argument. We put William (now age 6) in Muffy (94 M Reg Mini 1.3i) from birth. Shopped/drove all over the south of the UK with him in the car seat. By age 4 he had done more London to Brighton runs in either Muffy or Magnus (67 E Reg Austin Cooper S 1275) than a lot of others (three
A MINI has "got" to be safer/more agile/better constructed than a Mini, it goes without saying.
Besides, like the big 5 series BM ad says, you need to redefine the definition of "avoidable" accident!
cheers...magnus2