Is this going to be your forever home? Include space you can fit a lift into and storage for a mobility scooter / wheel chair - you may never need either but if you do you will be glad you did.
My HA property was built for people with mobility difficulties, and I don't know if these are standard now, but low light switches and high plug sockets, all doors 1 m wide.
Insulation and the most efficient heating, solar panels, windmill, whatever you can do to bring the bills down.
Charging points for 2 cars, or at least all the electrics for it.
Because of arthritis the only exercise I can realistically do is in water so if I had the space a swimming pool or if I didn't then one of those mini pools where there are water juts and you can swim without going anywhere.
I'd love a pantry, my kitchen faces west and in summer everything not in the fridge goes off.
A self cleaning toilet - you have probably never even thought of it but think about never cleaning a toilet again. If you go for the Japanese ones you can can get rid of toilet roll and have a warm water wash and an air dry.
Central locking. No checking windows and doors, just click you key like you do with a car. You can also link to the fire / smoke alarm so that in a fire the doors / windows unlock for you to get out.
How old are the children? If they are small then think about a child sized bathroom suite, either on its own or put in child sized toilet next to an adult sized one, the same for a wash basin so they can go to the loo and wash hands without needing a step.