The short answer
Plan for boredom rather than for entertainment, bring more food and more spare clothes than seems reasonable, and build in stops you do not need.
- A bag of small new things, produced one at a time rather than all at once. Novelty is the resource, not quantity.
- Food, constantly. Snacks in small portions in a container they can reach.
- A full change of clothes each, plus a spare top for you, in a bag you can get at without unpacking the boot.
- Wipes, bags for rubbish, and a roll of kitchen paper.
- Stop before you need to. A break every couple of hours costs less time than dealing with what happens when you do not.
What will ruin it
Never leave a child alone in a car, even briefly, and never in warm weather. The inside of a car heats far faster than people expect, and it is dangerous in conditions that feel mild outside.
Why it works
Small children have no sense of journey length and no way to self-regulate boredom. The plan that works is one that assumes that, rather than one that hopes they will cope.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.