My husband spends more on the first household because there are more children. Is that fair to me?

Fairness in maintenance (nafkah) is measured by the needs that are met, not merely by equal amounts of money. A household with more children does need more spending, and that is no injustice to you as long as your needs and your children's are also properly met. The problem arises if your basic needs are neglected while the other side is excessively favoured. List your needs clearly and discuss them with your husband in figures, not on the basis of feelings alone. Allah commands us to “stand out firmly for justice” (Surah an-Nisa' 4:135). If your right to maintenance is truly being neglected, consult the religious affairs office or the Syariah Court. See maintenance.