Uncle Dave/Meet Jennifer
Your always carefully avoided your nieces. Not because you were attracted to them (until recently the oldest was almost just a toddler) but because it is better to be safe than sorry. Your family eventually began to realize you did not look all that confortable around kids and to chat about it behind your back.
While your parents and John are in the kitchen preparing the turkey your step sister is having troubles yet again with Jennifer. Your mother steps in "Dave, help a little and take care of Jennifer please" and leaves. Jennifer's mother grinned a little and happily leaves to take care of Malena.
Jennifer has mid long light hair and green eyes. Always active, always moving she is used to being screamed at and to have adults look at her with either anger or frustration. Yet when you look at her slim and energic little body the emotion that arises is ... none of those. One way or another she realized it too. She had watched you from the distance a few times, not really sure how to deal with that weird distant relative and had not dared approach you until now. But now that you are supposed to watch over her she looks at you, curious (although still a bit excited from the fight with her mom).
You have zero experience with kids but you know an easy way to calm a kid
On the other hand this could be a one time opportunity