Easy ways to make money for kids

Woodcutting- If you wish to woodcut, then I suggest get your woodcutting over 70 to 75 by cutting willows and then go chop some yews. Yew logs sell for 459 coins each,(sometimes higher or lower) and are almost always in high demand by players training Fletching, Firemaking and Magic. It is very efficient, but this method is popular, so be careful of other people who has higher woodcutting level.

Fishing- Fishing Lobster, Tuna or Swordfish is a great way to sell, despite the going to Karajama and back. The only free-to-play spots at which to catch lobsters are a fishing spot on Karamja and in the Wilderness. If you have an explorer ring, it would allow the process to be faster. If you are fishing lobsters on Karamja you can sell the lobsters at the Karamja general store for a reasonable price. There is also another way to not leave the island but note your fishes, just go west of the Karajama general store and you should see a person named Stiles, who will note your fishes for free.

Mining- You should mine iron, coal, gold, mithril, adamant, and runite. They are the ores that will get you fast money. For gold, you should go to the crafting guild which has 7 rocks. For mithril, and coal, you should mine at the mining guild. For adamant, you should go west of Lumbridge swamp or Al-Kharid. Runite, I suggest that you get a high combat level before you go mine it. It is really good money, but only available in the wilderness.

Combat- You should get a high combat level first before you go. About level 60+, if you are not then train on Hill Giants, which is a pretty good money, because of the big bones and limpwurt roots. You can also try Cockroach Soldiers if you have high combat level. If you are low on food, sometimes you can go to Barbarian village to get some trout or salmon by the power-fishers or you can go heal at the Monastery, which is free. If you are 90+, then you can go to the Wilderness volcano and attack the Greater Demon which drops various of rune items.