My DD is 6yrs old and has been with us since she was two. Each year we have direct contact with her half sister who is now 17yrs and has been in long term foster care for 6yr. The sister still has contact with birth mum but I am not sure how frequently. Although I dread the contact, it usually goes really well and the girls get along fine. Its always us who organise the activity and I am finding it difficult to come up with something that will amuse them both. In the past we have been to Disney on Ice, shows, ten pin bowling, museums. Does anyone have any ideas where we could go?
Is the older girl interested in anything in particular? Does your little one have any special interests/places?
You could try something like one of those pottery painting places (but limit your little one to one thing to paint and she has to allow her big sister to take her time).
If its warm enough, a rowing boat or a visit to a WWT reserve might work. On one of those interactive Science museums.
I would also look for opportunities for the big sister to look after the little one (eg. holding the bird seed while the little one feeds the birds). Its what my 17 year old likes doing with their 10 year old sibling. Its a big gap, but can be bridgable.
Best too find something where they can talk interact with each other contact is about catching up talking, National trust is OK, castle, big park with open space , tea room's , play park, lots of space too run around . picnic , weather permitting.