Vacations can be a bit of a challenge for any large family. It is entirely possible for a family with foster kids to have wonderful vacations, there are just a few additional steps they must take. All trips must be approved by the caseworker and at times by the judge. Many large families get one hotel room, and the kids bring sleeping bags. However, foster families do not have this option as boys and girls are not allowed to stay in the same room. That said, I feel that vacations are extremely important for the entire family to take together even if it is a stretch to your budget. Do not place the foster kids in respite while you and biological children take a vacation. I think this is cruel at best.
When we go on vacation, we typically rent a house/timeshare and travel somewhere that is a reasonable drive from where we live. It's also important that a kitchen be available wherever we stay so that we are able to bring our own food. On vacation, we play board games, go to the lake, take walks to explore the area, et cetera. In years past, I have taken the kids to a theme park but, in my opinion, this was exhausting and expensive.
My best advice concerning vacations is that you should definitely go and take the entire family with you. If possible, rent a house to stay in and go to a place like the lake, the mountains, or the beach where there is a great deal that you can do outside with the kids for little or no added expense to the trip. They seem to enjoy this just as much as the hot, overpriced amusement parks. And trust me; there will be far more to your memories than just standing in line waiting for them to happen.