Would you stop a child from speaking because he/she is only 'allowed' to speak the words that he/she can read???!
I am not an instrumental teacher but I do teach children this age and I build up to the introduction of notation extremely slowly, gradually and systematically - then when the children ARE introduced to notation it is just the next tiny step along from what they have already been doing and they do it so easily and naturally that it is an absolute joy to see.
We are one of the few countries in the world who put our children into formal education so young and I can't see that this pays off in any way.
I studied 'The Teaching of Reading' as a subsidiary subject at college. Children have to have reached a stage of 'reading readiness' before they are able to comprehend these signs and symbols and to relate them to the sounds they speak - and there is a similar process involved in learning to read music.
We do not teach a child to read before it can talk. Why do we seem to think it is fine to teach a child what a crotchet is before it has any idea of the concept of pulse, or where an 'A' is on the stave before it has an understanding and awareness of pitch

?
Sorry, Louise1206 - I'm not getting at YOU - it's just that we have so many things in all aspects of education round the 'wrong' way and I am SOOO a Grumpy Old Woman today...
But my maxim, forever, is -
SOUND BEFORE SYMBOL.
Do please investigate approaches such as Dalcroze and Kodály - I think they will open your eyes to all the very many possibilities of both working musically without notation, and then how to use notation in a meaningful way to the child.