If you’re truly stuck for things to do with your child during the school holidays the best thing to do first is to ask other parents if they have any recommendations. This will firstly provide you with a first-hand testimonial about various places. Secondly, it’s a great conversation starter that can help you get to know some of the other parents. When your child is in the first few years of Primary-School, play-dates and parties are almost as much about how well you get on with the other parents as it is about how well they get on with the other children. So it is of vital importance to your child’s social development to ensure you develop good relationships with at least some of the other parents at their school. Also, if you get along will quite a few other parents and arrange several play-dates for holiday periods it’s surprising how quickly the calendar can fill up and you mind begins to be put at ease about what to do with the children over school holidays. 
Another good things to do is just do internet search for activities and days out in your area during the school holidays. I googled days out in Buckinghamshire and this was what came up:
http://www.dayoutwiththekids.co.uk/search.php?county=buckinghamshire
http://www.bucksfamilyinfo.org/kb5/buckinghamshire/fsd/family.page?familychannel=7
http://www.netmums.com/south-bucks/places-to-go
http://www.netmums.com/south-bucks/places-to-go
I got all this from just one search, so in the technological/ information age it’s definitely worth googling things. Remember to make your searches local, otherwise you could end up finding some brilliant days out 3-4 hours drive away!! This is fine if you decided that actually you’d like to book a hotel and make a family weekend of it. Just ensure you remain aware of the areas you are searching so you get results for the areas you desire. If you’re planning a trip to London, then obviously include this in your search; it’s just about remembering to type in all the key information.
A third thing you could do to find out what types of children’s activities your local area provides is check in with the local council; again this is best done through their website. I know Buckinghamshire has a local Families magazine that is free and usually given out at nurseries and schools. So it’s worth actively keeping a watch out for free local magazines for families as they’re bound to have a wealth of information in them about things to do locally with children.
It’s good to do a variety of different activities during the school holidays so your child/children have the opportunity to gain a broad number of different experiences. It’s always best to plan; first so you avoid double booking. Second, so nothing can take you by surprise that may put a dampener on things and you’re all able to get the most out of the experience. This way your child can enjoy a variety social, physical (sporty activities), creative and even cultural activities that will all go towards supporting his/her holistic development.
I would encourage and recommend that you have some quieter days where you don’t do so much. Either spend quality family time on these days, or simply use them as an opportunity to get things done around the house. The reason I suggest this is because children need to learn how to amuse themselves and if they’re always looking to you to provide them with entertainment then they’re not having the opportunity to use their own initiative, or imagination to look for ways themselves. As you know, initiative and imagination are two important characteristics that will contribute toward how holistically successful your child becomes as an adult. For further information about this please email me at: paula@paulaelizabeth.com