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We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measurewhite light flares in the young, moving group brown dwarfs 2MASSJ03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11), andreport on long-cadence (thirty-minute) photometry of a superflare in thePleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projectedrotational velocity ($45$ km s$^{-1}$) confirm 2M0335+23 is inflated ($R \ge0.20 R_\odot$) as predicted for a $0.06M_\odot$, 26-Myr old brown dwarf $\beta$Pic moving group member. We detect 22 white light flares on 2M0335+23. Theflare frequency distribution follows a power-law distribution with slope$-\alpha = -1.8 \pm 0.2$ over the range $10^{31}$ to $10^{33}$ erg. This slopeis similar to that observed in the Sun and warmer flare stars, and isconsistent with lower energy flares in previous work on M6-M8 very-low-massstars; taken the two datasets together, the flare frequency distribution forultracool dwarfs is a power law over 4.3 orders of magnitude. The superflare($2.6\times10^{34}$ erg) on CFHT-PL-17 shows higher energy flares are possible.We detect no flares down to a limit of $2 \times 10^{30}$ erg in the nearbyL$5\gamma$ AB Dor Moving Group brown dwarf 2M0355+11, consistent with the viewthat fast magnetic reconnection is suppressed in cool atmospheres. We discusstwo multi-peaked flares observed in 2M0335+23, and argue that these complexflares can be understood as sympathetic flares, in which a fast-mode MHD wavessimilar to EUV waves in the Sun trigger magnetic reconnection in differentactive regions.

K2 Ultracool Dwarfs Survey II: The White Light Flare Rate of Young Brown Dwarfs