Ds1 in Reception (turned 5 in Jan) likes writing little stories and messages. He makes up the words he can't spell phonetically, so for "Mamma" he writes "Mumu", which I can see why he does, or Saturday will be spelt "Sataday".
Anyway, we do work on spellings and reading and many of these words crop up then, but, when he has spontaneously written a story or a message I don't usually correct his spellings because I don't want to dampen his enthusiasm. But I'm wondering if maybe I should - although I fear this may put him off writing things. OTOH, if I don't correct him he will learn incorrect spellings.