Поставить из активного залога в пассивный ( passive voice); 1. some children follow the 'trick or treat' custom; 2. if people give them some money or sweets, they go away; 3. children parties offer amusing games.

1.The "Trick or treat" custom is followed by some children.
2.If some money or sweets are given to them, they go away.
3.The amusing games are offered by children parties.