Picture book fatigue

There seems to be a point, around the three to four year mark, when children have learnt favourite picture books by heart. Generally, the parents have too. My three year olds haven't been ready for chapter books but there doesn't seem to be a clear, or any progression, in picture books. Both children and parents are in need of fresh and slightly more complicated material.

I was first aware of this problem, many years ago, when my eldest son went to preschool aged almost four. The book for the first part of term was Eric Carle's The Hungry Caterpillar. A great book but one that my son had been given for his first birthday and been able to recite, almost word perfect, for probably more than half of his life. Of course, this may just have been to make the children feel comfortable in their new environment and they soon progressed to other books.

This problem has surfaced again. Our youngest, aged 3 and 1/2, knows many of his books by heart and to be honest, I've probably read some of them hundreds of times over the last almost 19 years. But he isn't quite ready for chapter books.

We've found some books which seem to fit the bill, and I would love more suggestions.

• Most of the Five in a Row books are in the "slightly more grown up" picture book group.

• The Katy books by James Mayhew have been tremendously popular here, both with Mr Exuberance and Miss Belle. Being able to spot pictures in art galleries has been a great "wow" factor.
• Fancy Nancy by Jane O'Conor. I really brought these for Miss Belle but her brother appreciates the humour and funny vocabulary.
• The lighthouse keeper series by Ronda and David Armitage

• Some of the old Ladybird books from the series about science. Water, Ducks and swans and Bridges have gone down well. Our youngest finds the history series too complex but his five year old sister loves these books.

I've got a few science type picture books on order and some other new books hidden. It does seem to be worth bringing out new books gradually so they can be savoured. I've also taken to hiding books for a while so when they re-appear they are fresh.

Has anyone else met "Picture book fatigue"? Any suggestions for counteracting this?