The only way for Pikachu to know Volt Tackle is to have learned it as a Pichu, which is possible only if one of the Pichu's parents breeds while holding the Light Ball. To have a Pikachu learn Volt Tackle, you need to start with a baby Pichu and acquire a Light Ball.
- Acquire the Light Ball
The only way to get a Light Ball in Pokémon Fire Red is to find it as a held item. The most common location to find a Pikachu is the Power Plant, where they can be found roughly 25 percent of the time. Alternately, a Light Ball can be found if the starting Pikachu from Pokémon Yellow is traded up to Gold/Silver/Crystal and then traded again to Fire Red.
- Pick the correct parents
To receive a baby Pichu, one of the bred Pokémon must be a female Pikachu. There are many other options for the male Pokémon, including another Pikachu, or Ampharos, Ditto, Plusle or Clefairy.
- Breed the two parents
In order to breed Pokémon, you must have seen or captured 60 or more Pokémon, defeated the Elite 4, received the National Dex from Professor Oak, and retrieved the Ruby from Mt. Ember. Doing so unlocks the post game Island four. The day care center can be found here. Leave the two Pokémon here, and proceed to walk around until they produce an egg. Remember to give one of the parents the Light Ball to hold while breeding.