A few more suggestions for maintaining the interest of kids:

• Colorful visual aids: campaign setting maps, town or city maps, and dungeon tiles or printouts. Miniatures or plastic figures are a big plus too.
• Appropriate fantasy-themed background music.
• Encourage the players to draw their characters with colored pencils or crayons.
• Fun props: costumes, foam swords, plastic gold coins, coin pouches, dice (not just the standard d4, d8, d10, d12, and d20 - let kids play with d5, d7, d9, and d11 dice or jumbo polyhedral dice if you have them).
• Funny accents and humor are always good. Monsters and NPCs should have unusual features or habits: scratching, warts, farting, etc. Don't be afraid to use the cliché Scottish accent for Dwarves, "upper class" British accent for Elves, West Country or Cockney accents for trolls and Orcs. Silly, quirky characters are good: the arch-villain sorcerer with a floppy toupee, the half-Orc barbarian bruiser with a cute kitten companion - who talks & calls the shots in a Master Blaster-type relationship.
• Don't let combat get bogged down with endless turns and modifiers - borrowing a page from Dungeon World wouldn't be a bad idea. No initiative rolls or specific turn order for each player. Especially if there are more than three kids playing, they may get fidgety waiting their turn in combat. Let them all declare what they're doing at the same time.
• In addition to combat and roleplaying, some kids also enjoy purchasing stuff for their characters at the town market - going shopping, getting good deals, arbitrage opportunities! The gold coin props would be fun here. Plus kids will be practicing their arithmetic skills.

A few more suggestions for maintaining the interest of kids:

• Colorful visual aids: campaign setting maps, town or city maps, and dungeon tiles or printouts. Miniatures or plastic figures are a big plus too.
• Appropriate fantasy-themed background music.
• Encourage the players to draw their characters with colored pencils or crayons.
• Fun props: plastic gold coins, coin pouches, dice (not just the standard d4, d8, d10, d12, and d20 - let kids play with d5, d7, d9, and d11 dice).
• Funny accents and humor are always good. Monsters and NPCs should have unusual features or habits: scratching, warts, farting, etc. Don't be afraid to use the cliché Scottish accent for Dwarves, "upper class" British accent for Elves, West Country or Cockney accents for trolls and Orcs. Silly, quirky characters are good: the arch-villain sorcerer with a floppy toupee, the half-Orc barbarian bruiser with a cute kitten companion - who talks & calls the shots in a Master Blaster-type relationship.
• Don't let combat get bogged down with endless turns and modifiers - borrowing a page from Dungeon World wouldn't be a bad idea. No initiative rolls or specific turn order for each player. Especially if there are more than three kids playing, they may get fidgety waiting their turn in combat. Let them all declare what they're doing at the same time.
• In addition to combat and roleplaying, some kids also enjoy purchasing stuff for their characters at the town market - going shopping, getting good deals, arbitrage opportunities! The gold coin props would be fun here. Plus kids will be practicing their arithmetic skills.