Last school holidays I got some great ideas from these articles – particularly ways my partner could get involved with inside activities & not just outdoorsy things. They have kid-friendly recipes too which is fun for rainy days.
https://thefatheringproject.org/fathering-channel/?_sft_category=activities-with-kids
Hope this helps!

Old sheets and blankets make the best basis for indoor forts and cubbies – my kids could play in there for hours! Lego is also great, play dough or if you can manage it, boxes can be made into all sorts of creations (this might be a bit hard to transport though). Other than that kids that age love helping to bake things.

I taught my miss 4 how to paint a wall today ????

A packet of disposable plastic cups and a bag of ping pong balls are always lots of fun. They can either use the cups upside down as bowling pins or play a game trying to throw the balls into the cups.

A tub of playdough, kinetic sand, paint pens and colouring books, sensory toys, books, cooking or baking, hide and seek indoors,

Parks, gymnastics, swimming, play dates, playdough or kinetic sand play, arts and crafts,

Discovering new parks if it’s not raining (take old towel to wipe the slide/swing if it has been raining)! If it’s wet get the gum boots and raincoats on and jump in puddles. My kids love it.

Making cubby houses at home. Movie afternoon (close the curtains, make popcorn)

Board games and playing card games always kept us busy on rainy days.

As cheap alternative to indoor playgrounds (like for example Lollipops) we also like to visit Bunnings where they have an indoor playground and mum can have a coffee whilst watching the kids, or go for aa play and a small treat to MacDonalds or Hungry Jacks where they also have an indoor polayground

Both my kids are the same age as yours. I always buy those plaster things from kmart so they can paint for awhile. I try and get a lot of craft things so they can let their imagination run wild.
My kids also like play dough and slime so making their own is always a novelty and they get to play with it after.

A visit to Bunnings for cheap marked down plants and a few packets of seeds for the kids to plant. They love working out where they want to plant their finds. One of my children has a specific spot in the garden that he calls his garden-bed. We plant out the seeds and watch them grow. Buying herbs like chives and spring onions are fast and fun and the kids like to harvest for their dinner toppings. Planting in cheap plastic buckets which I have drilled holes in are great for Spinach and Parsley and Mint and with the handy handles they can be moved to catch the sun.

Baking was often my go to with my kids when they were younger but that can be tricky when on holidays

Also games like hungry hippos or twister might be fun.

Playdough! and some cookie cutters wtc.. so much fun for that age group and the magic marker colour in books… no mess is always a bonus..

Board games and kids card games for sure.

Some lego that they can “free build”, some puzzles, pack some waterproof overalls and gumboots and let them play in the rain or still go for walks outside.

Music and dance activities are also a good idea and burn up energy.

Board games are a must for holidays; good for kids and adults.

Yes plenty of board games, craft and paint activities and jigsaws ! and maybe you could book some indoor playgrounds, lollipops, bounce, bowling or so as well. I sure would take rainboots and rain coats as a walk in the rain can be lovely too !

Board Games & card games. Never fails to be fun for all.