Margaret is the only one I have a marriage date for -- she was 19 when she married. What marriage dates do you have for the others?
Baptized in August of 1826, George was just under age 6 at the time of arrival in New Orleans. He was the youngest of the ten siblings.
If you're looking at the passenger arrival record, the two younger children match the ages of the children of Philip (George's brother), who were born in Germany (and who probably died after arrival).
The sibling next in age to George (Eva) was about 9 years old, next was Christina, about age 11, the Margaretha, 17. The latter clearly was old enough to work (which she did, as a clerk in a bakery). It's possible that the younger two girls worked as well. If not, the likely caregiver was Philip's wife, who either already was at home with her two young children or who had just recently lost them.
In any case, by 1834 -- if Fred Guker's account is to be believed -- Henry was in St. Louis getting married and Philip was in Missouri or Illinois where his son Martin was born. That same year, Margaret was married in New Orleans. Margaret's working days no doubt ended before the birth of her first child in 1835.
What is the source for your information that Margaret, Julia, and Christine went north and returned to New Orleans?