The new i-Size regulations R129 now group child restraint systems by height rather than the child weight, this has been done to simplify the decision making process for parents.
Infant carriers are suitable from 0 - 76cm approx birth to 12-15 months. This is what was know at group 0+ 0-13kgs in the previous R44 04 standard. Currently this standard is still running and relates to infant carriers as R129 has not been adopted for infant carriers at this time.
They should be installed rear facing giving little one optimum comfort and safety.