A good walk that maintains the interest for younger walkers and goes to a proper mountain top is Ben Vrackie - not too far from you. It is described here
https://www.walkhighlands.co.uk/perthshire/ben-vrackie.shtmlI suggest, though, leaving it until clear of snow.
In the meantime, try East Lomond
https://www.walkhighlands.co.uk/fife-stirling/east-lomond.shtml. It's an ideal walk for testing how much the children enjoy walking!
My suggestions for what to take.
1. By far the most important piece of kit I have used when walking with children is SWEETS. "Yes, you can have another one. Let's get the bag out when we get to that rock up there" is the most powerful motivator known to mankind.
2. Water. Make sure they have some hydration.
3. Decent hillwalking footwear for kids that isn't a ridiculous price can be found at Go Outdoors, or you can do even better sometimes at Aldi or Lidl
4. Make sure they have good warm and waterproof gear. My son got wet on a walk once due to a duff coat. I can still remember the shock of finding that he was wet and cold, I felt awful! -
https://www.walkhighlands.co.uk/Forum/viewtopic.php?f=16&t=58567