How to encourage pronunciation of Y (e.g. yellow)

[SpawnChorus]

DD (2.9) pronounces Y as N. For example "yes" is "ness".

Are there any exercises I should practise with her? Or is this quite a common 'problem' for a child of this age?

dd 2.4 used to say lellow until a week ago, all we ever did was say 'yes yellow' and not make a fuss, then we noticed she was pronouncing it right.