Café au lait are harmless birthmarks that present as flat brown marks on the skin. If your daughter has only a few, there is nothing to worry about. However if she has 6 or more brown patches, you should bring her to see a paediatrician or dermatologist to ensure she has no other associated disorders.
In terms of treatment, café au lait can be lightened using a pigment laser. Numb cream can be applied before laser so the procedure is comfortable. This requires 3-4 monthly sessions and excellent lightening can usually be achieved. However there is a chance of recurrence over time.
In view of her young age, I would not recommend that she embarks on laser treatment yet as she will find the procedure uncomfortable, even with numb cream. If the marks still bother her and she wishes for cosmetic treatment, 10 years old will be a good time to start. Hope this helps!
Warmest regards
Dr Stephanie Ho, Dermatologist