MHRA want "buffered core temperature" but this seems to be being interpreted as "simulated product" from what recently inspected sites are saying. Whether this is MUST or SHOULD I don't know. I don't know whether MHRA have picked up on paedi packs in this regard yet. One site chose 100 ml water in an adult pack as a compromise, others are talking about adult and paedi pack simulated product into which probes are inserted. Obviously, monitoring air temperature gives you earlier warning, but some systems allow alarm delay and door open events to be recorded anyway and the MHRA line seems to be Alarm linits = 2-6C (water); 2-8C air