White fluffy mould

I thought it would be a good idea to use the space in my porch to stack some seed trays.  But unfortunately there is white fluffy mould all over the soil now.  I am surprised by this as being by the front door you would have thought there was enough air circulation, if this is what did it.  Used same soil on ones in conservatory, which is open to sitting room and hot no probs there.

They will probably be ok as had that on my onion soil under the cloche last year and they were fine, didn't know you were supposed to let some air in.

Is there a prevention?  Would it be lack of air circulation?

I use ice-lolly sticks for labels and where the juice is impregnated on the stick...(no...I didn't wash them!)...there's an area of white mould on the compost.
Doesn't do any harm but makes me think you've got something "edible" on your compost surface that the mould is munching on???
Could be the kids have watered your seeds with squash???!!!

soil and compost are naturally ram-packed with yeast & fungal spores and bacteria which is quite normal - yeast & fungus will always respond very quickly to sugars (the science behind fermentation and brewing  ) and any other biodegradable stuff which is how composting works!.  When you start seeing fluff and toadstools etc, the fungus are maturing to the stage of sending up fruit bodies