Clothes that have labels saying wash at 30 - is it because you can get machines that do 30 now and they're encouraging you to be greener? Or is it because the dye will run like mad if you wash at 40? Our machine is quite old and doesn't do anything less than 40, so I handwash all the stuff that says 30 (including baby clothes ).
Would it just be better to get a new machine?! The one we have was in the house when we moved in 6 years ago so goodness knows how long it had been there before then. I suppose it's green not to replace it, but then if it's using more energy than it needs to... ???
I wash everything at 40 degrees. If you are worried about the colour running wash it on it own first, which usually 'sets' the colour and its Ok for future washes. There's not much that will be harmed at 40 degrees (wool, cashmere, silk perhaps - but I'm guessing your baby clothes aren't made of that!).
I think it would depend on the garment to be honest. If its silks or wool I would stick to what your doing (40 could mis-shape them or damage the fabric). If its cotton or viscose then I dont see a problem. Can you take the risk and try them at 40? Do the shortest possible wash with low spin. HTH