For starters, there is the novelty factor. The relative unfamiliarity of another person can have a very stabilising effect on a kid’s behaviour. For example, if your aunt cared for your child every day, their excitement at being with them would soon wear off. You can be sure they’ll misbehave with them occasionally, as well.
Secondly, time is a factor. Unlike others, you can’t hand them back after a few hours. They also don’t spend the whole day with your kid, dealing with every challenge the child meets and ensuring that their schedule runs according to plan.
Finally, others may be able to provide a broader range of activities in an environment that also has more social opportunities. That’s one reason your kid is usually better behaved at preschool than they are at home.
If their behaviour is always different with you around and if it concerns you, consider if you need to change the way you manage them. These questions, with input from child psychologist Dr Richard C. Woolfson, could help you navigate their behaviour going forward.