Categories definitely move and shift around over time, I tend to create a separate category for something either if I want to protect money allocated to it from being swallowed up by something else, or when I want to monitor how much I'm spending on something in order to either cut down, or just plan future spending.
So for example, I started out with kids' clothing all merged and then separated out DS1 (teen) from DS2 & 3 (under 6) because I was spending the whole budget on cute tiny things and then DS1 would have a growth spurt and needs a whole new wardrobe of adult clothing and I would have a heart attack at the cost
So now he has his own fund, and I just let it build up until he wants to go shopping. He currently has €80 in it. I still spend the little kids' clothing fund in dribs and drabs as I see bits I like or as they need things, so that is currently empty (because I went over last month so borrowed from another category and did an IOU). I really need to do a separate shoe and coat category too come to think of it.
The other way around I had separated out toys, days out spending and kids' activities (which I used for stuff like art supplies/science kits) for ages, but recently I have just merged all of this into "family fun fund" because half the time I couldn't decide what category to put something in.
For school holidays I would probably do one of two approaches (have done both at various times depending on finances)
- School Holiday Entertainment fund, with target for next school holiday, calculated at however much per week. Then when the holiday actually comes, dole this out into the individual categories like weekend days out, food on the go, eating out etc. At end of holiday, delete target and set a new one for the next school holiday.
- When there is a school holiday in the month, when I'm allocating funds I just throw extra into the fun stuff/eating out type categories. Because DS1 has cash for his school lunch I tend to save on this so I can rake some of that back for holiday entertainment for example.
Actually there is a third one I would never be organised enough to do - make some kind of holiday spreadsheet with carefully costed activities for each week of the holidays and then save up for that!