Saying words wrongly

by Tina
(Ireland)

My 9 year old the past few months has started pronouncing his words wrongly words like branged home my book. Instead of i brought home my book,! There are several others
IE I sitted -sat
We drived -drov
These are only a few examples there are more academically he is doing very well teacher tells me he is slightly above average across the board. Ive spoken to his teacher and she hasn't noticedit. None of his family or cercil of friends . As i said this only a few months ago and was one word it concerns me that there are so many more. Any bit of advice would be helpful thank you.