Usborne "see inside" or "look inside" books (non-fiction) would probably appeal to both of them. There is a dinosaur one, also see inside your body, see inside space/castles/history/trains/recycling etc etc We have about 6 of them, they are all great.
How about Jeremy Strong? He seems to write for a variety of ages so some of the books might be a bit old for them yet in content but he has loads. Can't remember a single title off the top of my head though!
I only have boys but I used to read his books to a 4 yr old and a 7 yr old together and I am sure some, if not all his books would appeal to girls too.
Dcs are going to get a stack of books each for their birthdays. Ds1 will be turning 7, am going ot get Mr Gum and How to Train your Dragon I think unless anyone has any other ideas? He has read all Roald Dahl, a fair few Dick King Smith which he likes, we are reading Harry Potter together, he isn't fussed by Enid Blyton. Mr Gum at the childminder's is the only thing that really seems to have grabbed him as much as Roald Dahl does.
What do I get dd who will be turning 5? She has listened to most Roald Dahl along with her brother, she still loves Julia Donaldson etc (Tyranosaurus Drip in particular. She is dinosaur mad) but of course is growing up so I want things to bridge the gap for her and gently move her up. She is a pretty decent reader already too so one or 2 to encourage reading independently would be nice as she really enjoys just sitting down by herself with her books. Not princessy shite, that isn't her style! Plus a couple more to read together.