I am an elderly lady ,but remember holidays when the family was young. First and fore most tell the family where you intend to go.If all in agreement then keep them informed of the plans,make sure you ask their opinions of what sort of hotel,holiday camp, tenting,whatever,don,t spring it on them at the last moment,and try to say it will be fun because chances are there will be tantrums.Nearer the time write down a list of what each person is going to pack,let them read it and change things if they want to,after all it,s their holiday too. Make sure the person is with you when you pack and let them help.Save a spare case for all medicines and toiletries are kept together, double check before you leave.Have any vacinations done early if travelling abroad,there might be reactions that will hold you up.
If you plan to go self catering it,s the little things that you forget that can spoil a holiday,like salt and pepper,sauces that you have to pop out for and don,t forget tissues,toilet paper(a must).and kitchen roll.cleaning materials washing up liquid.Never assume these items will be available.If you have young children don,t forget favourite toys and games.
If you can do all this and remain sane you deserve a holiday,It took me a while but I learned the hard way.
Oh! and whatever you do, make sure all pets are taken proper care of.