<p class="MsoNormal" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 13pt; font-family: AppleSystemUIFont;">We present a photometric variability survey of 12 young T-type and 7 young L-type planetary-mass objects with masses <= 20 M<sub>J</sub> and ages <= 200 Myr using the New Technology Telescope (NTT) in the Js and Ks bands. The variability of L and T brown dwarfs reflects their inhomogeneous atmospheric structures as they are usually fast rotators. Atmospheric models reveal that surface gravity is crucial for shaping the atmospheric structures of ultracool objects. Preceding variability surveys suggest some correlation between surface gravity and variability occurrence rate as young low-gravity L objects have an enhanced variability rate compared to their field counterparts. Thanks to the recent detection of dozens of young T-type planetary-mass objects, we are able and aim to conduct a variability survey of young T objects for the first time and investigate the effects of surface gravity on the variability of L and T dwarfs in a large sample size. 5 new variables and 2 variable candidates were detected. Combining previous variability surveys of field and young L and T objects, we find that young objects are more likely to be variable than field objects. The variability occurrence rate of young T objects is more than twice the rate of field T dwarfs and the results of L objects are consistent with the previous study. Both field and young samples have higher variability rates at than outside the L/T transition. In conclusion, this study provides insights into the effects of surface gravity on the variability of L and T dwarfs, contributing to our understanding of the atmospheric structures of ultracool objects such as giant exoplanets.<o:p></o:p></span></p>