So we (me, DH and 2 DC) were round at my parents' house on Christmas day. Also present were my brother SiL and their 2 DC.
Due to space, during lunch, the 4 children (aged 4-8) were seated at a separate table in the lounge, the adults were at a table in the adjoining dining area (so we could see the DC and they could see us).
During lunch, my 2 DC sat reasonably quietly and ate their meals. My brother and SiL's DC ran about, jumped on the sofa and climbed over the tables and chairs. At no point did my brother or SiL do anything to stop them. My parents (who tiptoe round SiL for fear of being accused of "interfering") looked a bit worried for their furniture but also said nothing. After about 10 minutes of this, DD (who knows better) decided she might as well copy her cousins and got onto the sofa. Whereupon DH told her in no uncertain terms that she should get straight off and go back and sit at the table. Which she did.
At this point, SiL rather ineffectually "suggested" to her DC that they should also get down and eat their meals. They both sat down for approximately 10 seconds and then got up and started jumping about again. She then said rather vaguely to the rest of us "I guess they are just that age where they climb on the furniture, they love jumping on the sofa at home". WTF!!! AIBU to think that climbing on the furniture/jumping on the sofa is not an acceptable behavioural phase, but something that should be discouraged at every turn. Or have I missed some alternative universe where it is actually ok in some circumstances ...?