Problem: The term child labour can be misleading when it confuses harmful work with employment that may be beneficial to children. It can also ignore harmful work outside employment and any benefits children normally derive from their work. Domestic work is an example: all families but the rich must work at cleaning, cooking, caring, and more to maintain their homes. In most families in the world, this process extends to productive activities, especially herding and various types of agriculture, and to a variety of small family businesses. Where trading is a significant feature of social life, children can start trading in small items at an early age, often in the company of family members or of peers.
What can children do in countries were trading is involved?
The answer is the following: children can start trading in small items at an early age, often in the company of family members or of peers

Problem: Stockton and Kearny went on to recover Los Angeles and force the capitulation of Alta California with the "Treaty of Cahuenga" on January 13, 1847. As a result of the Mexican–American War of 1846–48, the territory of Alta California, including San Diego, was ceded to the United States by Mexico, under the terms of the Treaty of Guadalupe Hidalgo in 1848. The Mexican negotiators of that treaty tried to retain San Diego as part of Mexico, but the Americans insisted that San Diego was "for every commercial purpose of nearly equal importance to us with that of San Francisco," and the Mexican-American border was eventually established to be one league south of the southernmost point of San Diego Bay, so as to include the entire bay within the United States.
Why was the border between Mexico and the United States established one league south of San Diego Bay's most southern tip?
The answer is the following: to include the entire bay within the United States

Problem: Mathematics: The earliest traces of mathematical knowledge in the Indian subcontinent appear with the Indus Valley Civilization (c. 4th millennium BC ~ c. 3rd millennium BC). The people of this civilization made bricks whose dimensions were in the proportion 4:2:1, considered favorable for the stability of a brick structure. They also tried to standardize measurement of length to a high degree of accuracy. They designed a ruler—the Mohenjo-daro ruler—whose unit of length (approximately 1.32 inches or 3.4 centimetres) was divided into ten equal parts. Bricks manufactured in ancient Mohenjo-daro often had dimensions that were integral multiples of this unit of length.
The Indus Valley Civilization was the first to have traces of what?
The answer is the following: mathematical knowledge

Problem: Hospital Maciel is one of the oldest hospitals in Uruguay and stands on the block bounded by the streets Maciel, 25 de Mayo, Guaraní and Washington, with the main entrance at 25 de Mayo, 172. The land was originally donated in Spanish colonial times by philanthropist Francisco Antonio Maciel, who teamed up with Mateo Vidal to establish a hospital and charity. The first building was constructed between 1781 and 1788 and later expanded upon. The present building stems from the 1825 plans of José Toribio (son of Tomás Toribio) and later Bernardo Poncini (wing on the Guaraní street, 1859), Eduardo Canstatt (corner of Guaraní and 25 de Mayo) and Julián Masquelez (1889). The hospital has a chapel built in Greek style by Miguel Estévez in 1798.
Who originally donated the land for Hospital Macie?
The answer is the following:
Francisco Antonio Maciel