We observed strong superflares ( defined as flares with energy in excess of 10 ^ { 33 } erg ) on three late-M dwarfs : 2MASS J08315742+2042213 ( hereafter 2M0831+2042 ; M7 V ) , 2MASS J08371832+2050349 ( hereafter 2M0837+2050 ; M8 V ) and 2MASS J08312608+2244586 ( hereafter 2M0831+2244 ; M9 V ) . 2M0831+2042 and 2M0837+2050 are members of the young ( \sim 700 Myr ) open cluster Praesepe . The strong superflare on 2M0831+2042 has an equivalent duration ( ED ) of 13.7 hr and an estimated energy of 1.3 \times 10 ^ { 35 } erg . We observed five superflares on 2M0837+2050 , on which the strongest superflare has an ED of 46.4 hr and an estimated energy of 3.5 \times 10 ^ { 35 } erg . This energy is larger by 2.7 orders of magnitude than the largest flare observed on the older ( 7.6 Gyr ) planet-hosting M8 dwarf TRAPPIST-1 . Furthermore , we also observed five superflares on 2M0831+2244 which is probably a field star . The estimated energy of the strongest superflare on 2M0831+2244 is 6.1 \times 10 ^ { 34 } erg . 2M0831+2042 , 2M0837+2050 and 2MASS J0831+2244 have rotation periods of 0.556 \pm 0.002 , 0.193 \pm 0.000 and 0.292 \pm 0.001 d respectively , which we measured by using K 2 light curves . We compare the flares of younger targets with those of TRAPPIST-1 and discuss the possible impacts of such flares on planets in the habitable zone of late-M dwarfs .