Updated: Jan 2
You might think it is a question of saving money. Actually, not really. Washing your clothes 30 degrees, you might save 15/20 € per year no more. However, you will use less electricity and doing so, it is more ecologic.
The only real reason you should wash the clothes 30 degrees is to preserve them. Washing your clothes at low temperature will avoid the colors to fade to quickly. If there is elastane fabric in the clothe 30 degrees is the perfect wash to preserve it from braking.
More and more detergents are designed to work well on cold temperature. Check the packaging when you buy them. I would suggest a non-bio liquid as powder can leave marks. Baby clothes are not so dirty that they required a high temperature wash.
You might ask yourself, what about stains? Believe me, between milk, pukes, explosive poops and veggie purées, I know too well about stained clothes ; ) The trick is to not wait for the stain to dry before you attack them! You can use a stain remover powder or liquid and let the clothes soak for a while. You can also use white vinegar to soak the clothes or do a quick pre-wash with Marseille soap. They all work well on the stain. The wash will do the rest and even at 30 degrees clothes will be completely clean.
Off course, for toddler underwear, socks or even short and t-shirt when they sweat you might prefer a higher temperature wash.
Remember to always check the tag to respect the manufacturer instruction.