I am 20 years old unmarried girl
My paternal uncle is going to perform Umrah with his wife and his two less than 10 years old kids
Can I go with them to perform Umrah?
Allah the almighty says:
Prohibited to you [for marriage] are ... your brother's daughters, your sister's daughters, .... (4:23)
This means your paternal uncle is a mahram and you can therefore join him and His family to perform 'Umrah if your guardian (father, husband …) allows you to do this sunnah.
See also in the fatwa islamqa #316:
The ulamaa have listed five conditions for a person to be considered a mahram. He should be male, Muslim, adult, and of sound mind, and he should be a relative to whom marriage is permanently forbidden, such as a father, brother, paternal uncle, maternal uncle, father in law, mothers husband or brother through radaaah (breastfeeding), etc. (as opposed to relatives to whom marriage is temporarily forbidden, such as a sisters husband, paternal aunts husband, maternal aunts husband).