Erhua and reduplication
In spoken language, northerners do say 一点点儿 or 一点儿点儿 sometimes, but not all the time, it depends on the situation. It is not wrong to say those words with erhua.

However, I don't encourage Chinese language learners to learn them because 


it is not really that important 
it doesn't really change the meaning 
it is hard for learners to say them in a natural way 
you don't have to sound like a northerner.


I believe correctness is more important and sounding natural.