It depends on where you are going, what the weather will be like (swimshorts and tshirts take up far less room than bulky winter coats).
Firstly pack a bag with various first aid bits and medicine. A good thermometer, some calpol, disinfectant wipes, plasters, bite cream, insect repellent, suncream (maybe rehydration sachets, depending on where you are going). Then make sure you have travel insurance.
Then pack things to make your life easier, like a cloth travel high chair (depending on age of your dc), muslin squares, whatever. Speak to your family and see if they can borrow kid stuff you might need, or get it off fb marketplace locally.
If bringing gifts for family then make sure they are super small, and not taking up half your suitcase.
Clothes - pack about a weeks worth for you both, it can all be washed.
Basically as long as you have good travel insurance, some emergency medicine, clean underwear and a couple of outfits you'll be set. If you do find you need more clothes then just go to a cheap shop like primark/C&A.