In addition to the weight (40 kg (6 stone/88 lbs.) per donkey maximum), think about the volume, too. Your kit should be as compact as possible. I will provide you with a pocket scale so that you can re-evaluate the load during your hike.  

• Here are some things to avoid in order to keep your kit as light and compact as possible:

Avoid Tetra Paks” of UHT milk. Pack powdered milk or tubes of condensed milk instead.

Avoid large cardboard boxes and half empty packages (like breakfast cereal).

Choose quick-cooking rice or noodles, with small tins or packs of concentrated sauce or bouillon cubes, rather than canned prepared food.

Take the bare minimum of pots and pans. A pot can double up as a wash basin, for example.  

Toiletries: Take travel-sized rather than standard-sized bottles. Put a bar of soap in a plastic bag rather than a rigid box. If you’re hiking with a group don’t double up: shampoo, toothpaste, etc. can be shared!

If you’d like your child to be able to ride on the donkey’s back sometimes for a rest, plan to have the baggage on top of the donkey’ saddle be a rucksack. That way, you can take it off and carry it on your own back to make room for the child.