Therefore, according to the Swedish Food Administration, the intake of the usual cinnamon (cassia cinnamon) in children should be limited to a maximum of 0.5 teaspoon per day.
Ceylon cinnamon, on the other hand, contains much less coumarin than cassia cinnamon. This means that you do not need to worry about the intake of Ceylon cinnamon, as the difference in coumarin content is very large (about 2500 mg/100g versus 17 mg/100g).
Therefore, I recommend using Ceylon cinnamon when baking for children. To be on the safe side. However, there is no risk to consume more cassia cinnamon in a single day, it is a long-term high dose that is dangerous.
Read more at the Swedish Food Administration (search for cinnamon), they have a risk report on cinnamon among other things and there are guidelines in their report on foods for children.