ccrash is right – it’s usually written “tow-head” or “towhead”. the word “tow” meaning light-colored dates back to about 1601, and the combination “tow-head” dates to around 1901.
when i looked it up, the OED said in addition to meaning light-colored hair, it also refers to “also an unkempt or tousled head; a person having such hair” – i had never heard that definition before.
one of the earliest references is, “Little Europena, with baby wisdom, put her tow head under the cloth.” (A. H. Rice 1901) – what an odd thing to say, huh?
also for me personally, ‘tow-head’ has the connotation of very light almost white hair that will most likely turn darker as the child ages. that wasn’t in the OED, but i guess i think of it that way, because tow-head almost always refers to children. you never hear anyone talk about a grown man or woman with platinum hair called a “towhead” – it just sounds odd.