The injuries you describe are getting close to 'GBH' (rather than 'ABH'), so 'harm' is likely to be classed as 'high'.
Kicking someone in the head is regarded as adding to the seriousness of an offence. (In the case of 'GBH' it would almost certainly upgrade the offence to 'GBH with intent'). So 'culpability' is likely to be classed as 'high' (particularly as the offender acted as part of a gang, which again adds to the seriousness).
So the Magistrates Court is likely to pass the case to the Crown Court because it's a 'Category 1' offence. That would mean a 'starting point' sentence of 18 months imprisonment, reduced to 12 months if there's an early guilty plea.