Hi Dim,
Good on you for planning to get your kids out there - starting early is great!
It might be good to go car camping one time, just to get them used to a tent, before you do an overnight walk. If you do too many new things at once... well some kids find it overwhelming. Or at least make their first overnight walk very short, say 1-2km so you can always pull out easily if you have to.
With regards to gear, we didn't buy anything the first time and just chose from the clothes and gear they already had. Start SIMPLE, and if they love it then build up your gear slowly. Focus first on the things they won't grow out of or can wear every day anyway. Since those early days our kids now they have their own packs, walking poles, snow shoes, thermals, etc.
We took our younger two daughters for their first overnight walk in June (winter!) a few years ago. They wore a whistle on a lanyard around their necks and used small/school backpacks with headlamp,change of clothes which were used as PJs or spare dry set, day snacks, water bottle (filled to 1/2 L), soft toy, and the warm and waterproof layers worn or stuffed into the top of their pack. From memory, their packs weighed around 2-3 kg. Apparently, the weight guide is about 25% of body weight but we wanted them to be happy so they only carried the minimum. Can't remember if they also carried their sleeping bags. We carried everything else, shelter, cook gear, food (lunch/dinner/breakfast), some wood for a fire, etc.
Don't take too much for you or them. One set of clothes to be worn, the extra layers to keep warmer and dry (eg. parka, beanie, gloves, poncho), and a set of thermals (or leggings and skivvy) to change into for bedtime if your clothes get wet.
Watch the weight and space in your pack in case you need to pull some things out of theirs to lighten their load.
Shoes - They wore their sneakers with woollen socks - and carried a spare set for sleeping in. Think they also took crocs for camp shoes in case their shoes got wet. Kids are typically much less fussy about getting wet and muddy, so we didn't worry about waterproofing since their sneakers are mesh anyway. You could use bread bags between two layers of socks as a cheap solution if you want.
We walked on a trail so we didn't worry about gaiters, as they were wearing long track pants.
There was no rain forecast, so we took some cheap $2 disposable plastic ponchos for the kids just in case.
Cutlery/crockery - just take some disposable paper (great as fire starter for campfire) or plastic. If you are doing simple pasta or rice, a disposable plastic spoon is lightweight. We have plastic bowls that fit inside our bushwalking pot and some of those Light My Fire sporks which the kids found exciting but I wouldn't rush out and buy them, it is just that we already had them. Or try the knoons that come with packs of kiwi fruit from the supermarket - knife and spoon combined.
Suprise treats - this worked well for motivation, eg. marshmallows for roasting on the campfire (a special treat for them since it was winter, not really my thing) and for hot chocolate in the morning, jelly bears for energy on the trail (a real treat from me as I usually go for healthy food), dinner food they love, etc.
If I forgot to answer any of your questions, just ask away.

- All set for first overnight walk
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