According to the packaging, the recommended age for using Mosquito Milk insect repellent on children has just jumped from 3 years to 13 years. We've not been notified of any change of formula so we suspect this is a bi-product of the planned changes to EEC Biocidal Product Regulations.
These new EEC Biocidal Products Regulations (which includes all insect repellents) are due to come into force in the UK in 2 years time after a phase-in period. Then the use of DEET based insect repellents will be severely limited both in concentration and recommendations for age and application. The regulations have already limited the number of chemicals that can legally call themselves an 'insect repellent' to four. These regulations may come into force earlier in other parts of Europe (where Mosi Milk is made). The active ingredient in Mosquito Milk is DEET at about 20%, a low concentration by current UK standards.
To balance this the US regulatory body the Centre for Disease Control, while doing further research, still gives the advice that DEET should not be used on children under 2 months and that a concentration of less than 30% DEET should be used for children aged over 2 months.
It looks as though this particular change has taken place more in Brussels, than Mosi Milk.
Our advice is that the top priority is to prevent children getting bitten, especially in areas where there is a disease risk. Use low concentration DEET if you need to, but Saltidin (Picaridin) or Citriodiol repellents such as Expedition Sensitive (2 yrs) or Mosi-Guard Extra (6 mts) are suitable for young children and have proved themselves very good repellents.