Plan the total back-to-school shopping budget.
Back-to-school spending divides into per-child costs and shared costs. Uniform, supplies and shoes scale with the number of children; a laptop or tablet often does not, so entering it separately stops the estimate inflating with each additional child. Dividing the total by the months available converts a lump sum into a savings rate, which is the number that actually prevents the spend landing on a credit card in the last week of August.
Budget
Total = (clothing + supplies + shoes) x children + shared technology
Savings rate
Monthly saving = total budget / months available
Clothing and footwear, typically over half the per-child total, because uniform items are bought new and outgrown annually. Stationery is the smallest line and the one most often over-bought.
Buy uniform second-hand where schools run exchanges, delay non-essential stationery until teachers publish actual lists, and stagger technology purchases outside the back-to-school period when prices are inflated.