Buy second hand books/clothes/toys etc. Declutter unwanted items, so that someone else can enjoy them before they become obsolete/unfashionable.
Turn the central heating down so it's background level. Wear jumpers/gilets/wristwarmers. Invest in loft insulation, double glazing, draught excluders... the payback is much quicker than leaving it in a savings account.
Take meter readings every morning... aim to decrease it each day.
Grow your own veg and fruit. Get an allotment or join a community growing scheme if you don't have a garden.
Go on a community family tree planting day.
Eat a local, seasonal diet that's a balance of meat and veg. Children need animal products to physically and intellectually thrive. Many vegan kids have failure to thrive, look gaunt and have weak teeth and bones. (Lots of sad ex-vegan narratives of longterm deficiencies coming through now on youtube/instagram etc). Try to buy from independent shops, market stalls or community co-op schemes, rather than supermarkets. Also look out for zero waste shops, where you can buy your shampoo, washing up liquid etc in refillable bottles and dry goods in your own tubs. Take your own tupperware to the butchers to save on packaging.
Don't buy bottles of soft drinks. Kids only need water and milk, unless it's a birthday party/Christmas etc. Adults also tea/coffee.
Don't buy industrially processed food like seed oils, sugar, snack food etc. Think of all the land and destruction of habitats required for huge food factories, distribution centres, logistics parks, packaging manufacture, high tech machinery etc required for complex food products. Snack on simple things like fruit, nuts, local cheese etc.
Walk or cycle only for shortish distances.
Don't fly on holiday.