There are local hot spots if you don't mix the milk after microwaving.
Babies really do get burned by microwaved milk; there is an actual danger the medical community is trying to prevent when giving advice not to microwave milk.
The danger is due to a combination of hot spots within the milk and the container being cooler than the milk itself. If someone just feels the outside of the container they may misapprehend the temperature of the milk, resulting in the baby being burned.
Microwave heating of infant formula: a dilemma resolved Pediatrics (1992) vol. 90 pages 412-415.
Microwave heating of infant formula is a common practice despite concerns of infant scalding....Topmost portions reached a mean temperature of 44.7 +/- 1.7 degrees C and 43.0 +/- 2.4 degrees C for all types of 240-mL and 120-mL bottles, respectively. Topmost temperatures were significantly hotter than temperatures reached at other sites. Routine mixing resulted in formula temperatures which could safely be fed to infants (35.4 +/- 0.3 degrees C and 33.9 +/- 0.2 degrees C for 240-mL and 120-mL bottles, respectively).
Risk factors for microwave scald injuries in infants. Journal of Pediatrics (1984) vol. 105 page 864-867.
An infant sustained second- and third-degree scald burns of the oropharynx from drinking formula heated in a microwave oven. The circumstances leading to the scald injuries were recreated. Factors contributing to the injury included the volume of formula, the initial temperature of the formula, and the temperature gradient between the liquid core and the bottle surface after microwave heating.
Burns associated with the use of microwave ovens. Journal of Microwave Power and Electromagnetic Energy (1992) vol. 27, pages 160-163.
burns can result from the ingestion of microwave heated food because consumers may overlook the differential temperature gradients within foods and between the food and the container.
Other related articles are:
Burns by ingestion of milk warmed-up in a microwave oven Archives of French Pediatrics 1988 vol. 45 page 439.
Aerodigestive tract burn from ingestion of microwaved food. Case Reports of Emergency Medicine (2013) article 781809.