Canon 85 1.8 vs. Canon 100 2.8 L vs. Canon 135 2.0 L: Which one is best for indoor?

the EF 50mm f/1.4 is a good choice for kids indoors
very sharp on the 6D

shedberg wrote in post #16548381
I hate to say it, but it's going to be way too long for your living room...

+1

Unless your living room size is similar of New York Central Park

135L is a little long for anything other than headshots or tight candids inside - Depends how big your rooms are though obviously.
I use 50/1.4 & 135L - I found the 85mm too close to 50mm [although the 85/1.8 is a slightly 'nicer' lens] I was going to go with the 100/2 but my other half suggested I just get the 135L straight out as it's a lens I'd always wanted & she knew a 100/2 would last me 6 months before it went for a 135L anyway....

I think you've made a good choice based on what you already have.

My experience on FF is 135mm outdoors and 85mm indoors.

Best for indoor (smaller spaces as indoor sports) is IMHO:

50L
35L or sigma 35 1.4 (no experience with those but heard more good things about the sigma)
Only headshot portraits or torso: 85L

For a budget:

50 1.4 (canon or sigma)
35 2.0 which you own
Headshot and torso: 85 1.8 (must also be a great lens from ehat ive heard)

Greets
David

Shorter focal lengths will work well for full body portraits or groups, but shouldn't be used to enable shooting people from less than 2.5m, as that would lead to excessive perspective distortion.