There are 2 ways to get bombchus early. The most common way is to get them from Child Spirit Temple. The other way is to get them from Bottom of the Well.
Entering Bottom of the Well Early Edit
To get early chus from bottom of the well you must first get into BotW early with a cucco dive. Take a cucco and hit it 4-5 times so it's almost ready to attack you. Now throw it on the rim of the well and get on the opposite side of it then jumpslash it. It should activate the cucco attack cutscene before you hit the water and you'll fall right through to the bottom. If you're skilled then you could activate ISG off the cucco and shield drop backflip into the Well.
Set up and Clipping Edit
Now that you're in the Well, go to the back and play Zelda's Lullaby on the triforce emblem to lower the water level. Go back to near the front where the pool has drained and go in the crawlhole leading to the room before dead hand with the skulltula and climbable vines. Now heres the tricky part, you have to use the skulltula to clip you through the vines unto the unloaded basement. Go to the very left of the vines and climb up so the skulltula doesn't hit you. Now move slightly to the right but not to the middle. Now prepare a spin attack. The skulltula will be bouncing up and down, try to release the spin while its up. When you release immediately press Z and hold back to get back on he vines. Quickly climb down 2 rungs then press A to drop, then press down and up quickly to grab the vones again before touching the ground. If you did it right the skulltula should hit you and you will go flying out of bounds. If the spin attack method is too hard or you already hit the skulltula once (remember they only have 2 HP) you can use deku nuts. Once you stun him climb up 2 rungs then when you think its about to unfreeze, drop down and press up/down to grab the vines again and hopefully you will clip.
Jumpslashing to the chus Edit
Depending on your position when you clippd you could land in 1 of 2 places.
- On the ground in the basement.
If this happens then try moving forward until you see textures of the acid pool. Near the tip if the visible texture there will be a patch of invisible water to swim in. Go in and face forward, press Z, hold down/down right on the control stick and mash B. While rising up you should clip through a small corner and apear at the top of the water. Now look forward at the room with the chest. Swim toward it and you will fall out of the water, now jumpslash. If you did the jumpslash at the right time you will get warped in the room and can gran the bombchu chest. Don't worry about the rubble at the top of the vines in there, its only solid from the front so you can easily just climb out. The jumpslash can be a bit tricky but theres a way to make it easier. Right before or as soon as you fall out of the water pause. You have to jumpslash 3 visual frames after falling out of the water so pausing can help. This trick is called pause buffering.
- In invisible water.
If you do this then don't move and let yourself rise up to the top of the water. Sometimes you'll fall in invisible water but still be in bounds in which case you'll have to swim out of the water and do #1. The water is the same path as it would be if the water wasn't lowered so use C up to look up to see the path and follow it until you're near the room with the chest in it. From there just do the jumpslash in. If you mess up the jumpslash then you could just use the steps in #1 to get back up.