the reason dentists say not to use toothpaste until they are 2 is because of the fluoride. Too much fluoride can make kids sick and they shouldn't be swallowing it at all. A basic rule of thumb is no fluoride toothpaste until they can spit it out.
Milk teeth toothpaste is low flouride so if you use a tiny smear, and I mean tiny then they are ingesting a minimal amount. It is for ages 1-6.
Some flouride is actually good for dental health, neither of my kids have dental decay (ages 3 and 6) and their health is great.
This actually says introduce milk teeth toothpaste at 18 months. Provided your kids arent eating the toothpaste and you are using a tiny amount, it is very beneficial for dental health.