Bf, put them outside during the day even if it's 10C. The sun will do them more good than the temp will harm them at this stage of their lives.
To help them along, invest in some bubble wrap. Put the pots in a crate or similar, erect props of some sort in each corner (higher than the tops of the plants) and use the bubble wrap over the top to create a mini greenhouse. It will add at least 5º to the temps inside the bubble wrap.