Three Weeks, Three Kids (2011) on Netflix

Plot summary

Mandy Norton married young and settled into family life with her husband Brian and their three children, Alice, Flo and Miles. Her younger sister Jennifer, 25, lives free of commitment and is glad her boyfriend has not proposed. Their mother Kathryn believes Jennifer's carefree habits conceal a fear of settling down. When Mandy and Brian arrange a three-week vacation in Europe without the children, Kathryn asks Jennifer to stay with the kids until she can get to town. Jennifer finds that caring for three children is harder than she expected, and that keeping her sister's trust means becoming the one who sets the rules rather than the fun aunt. Will Johnson, the new neighbor across the street, lends a hand.