Mishti getting upset over her mother not being to give her time very often is very natural for a 5 year child to react. My own cousin brother is 5 and he often complains to his father avout how he is always busy and they don't get to spend time on special days. Even they get angry just like Mishti.
Hell even I get upset at times when something like that happens when plans are made by keeping everything in mind and last moment emergency ruins them.
The girl made plans and it's normal for a 5 year old to get angry, cranky and upset for the moment when she listens that they won't be doing anything as per plan.
But good thing is that she listend after that and felt bad for her rude behavior almost immediately in her room.
Just give some credit for actual human behavior here.
Comparing how Kunal behaved is an insult to the innocent behavior of Mishti.
Children do get upset when their working parents don't get to spend special time with their parents. But they understand that too once they let out their frustration and that's the good part. Mishti isn't behaving like a brat here but just as any normal child.