Or if you must buy designer clothes, get them at a discount outlet.
Children's clothing in particular can be very expensive and kids don't stay in them for long. Unless you are living in a really upmarket area, children won't know what brand clothing they are wearing (and if you are in a really upmarket area you probably won't be needing budgeting tips like this one).
Buy clothing out of season at department store stocktake sales, just remember to get a size or two bigger for children. Check eBay or second hand stores - eBay in particular will often list brand new items at well below store prices, even including postage. Accept hand-me-downs from relatives or friends with older children.
There is no reason at all you need to pay full retail price for baby or children's clothing.