How often should a child's hair be cut?

I have a four year old with hair down to her almost, but it tangles like nobody's business. She's multiracial so I don't know if that has anything to do with it. She has loose curly ringlets and when her hair is wet, it looks straight (if that can give you an idea of her texture). I have only clipped her ends once. Am I supposed to be clipping her ends often? They don't look split but i'm wondering if that's where the tanglings coming from. She can spare a nice trim because of the length. Should I take her to a kiddie salon and have them take off an inch or two? What do you think?