Most of these are here for my own guidence, though they may be of use to others making RPG campaigns for kids.
D&D Beyond: Play D&D with kids using the Young Adventurers Guide
D&D Compendium: DMing for kids
Tribality: Playing D&D with kids and how to do it properly
Dungeon Master's Vault: Family friendly D&D modules
Drive-thru RPG: character sheet for young players
Alchemy RPG - New virtual tabletop supporting many of the top RPG platforms.
D&D Beyond - The official D&D virtual tabletop from Wizards of the Coast.
donjon.bin.sh - Many random generation resources.
Dungeon Scrawl - Dungeon map making tool. Nice, but most features have crept over a paywall. Subscription is a little pricey for casual use.
RPG Map Editor II - Intuitive pixel style software for creating dungeon, building and town maps. Can import from Procgen Arcana. No longer in development and assets are few, however you can create your own.
Watabou's Procgen Arcana - Open resource for generating random maps with markup. Regularly updated.
Inkarnate - Complex map creation tool.
Dungeon Map Doodler - Map creation tool with a hand-drawn asthetic.
Google Docs - Used for quickly sharing ideas.
Google Slides - Used to quickly share ideas if the person didn't understand what you wrote in the doc and needs you to literally draw them a diagram.
Pixlr AI Image Generator - Used to create pictures for your campaign if you can't draw and don't have any artistic friends to give you a hand.
Pixlr Express - Used to draw over the AI art to make you feel less guilty about using AI art.
Krita - Used when you realise Pixlr Express is a bit crap and you need a proper art app if you want to make anything decent.