Emilie, 9, and Amie Miller, 11, from the Young Carers Group, pushed the button just after 6pm and watched the strings of lights on the Weighbridge roundabout come to life.
Emilie has battled with progressively worsening hearing loss and severe anxiety, but has never given up.
Amie has suffered from severe anxiety for a while now and fights through it every day.
Both are caring towards each other and also help with their little brother, six-year-old Riley, who has a rare chromosome disorder and special needs.
Amie said they had seen the lights illuminated before, but never seen them switched on.
‘We are very excited,’ she said.
Their mum, Becky Pyle, was with them for the switch-on.
‘It is really nice to be able to recognise what the two girls do,’ she said.
‘It is difficult to have a brother with special needs. They are so special.’
The tree is organised by the Rotary Club of Guernsey and this is the 16th year the mast has been used to create a light tree.
Club president Dave Parish said the tree was a very important symbol.
‘It’s vital,’ he said. ‘It indicates the start of all our Christmas initiatives. There is the distribution of presents to needy children. There are also our flag days on Friday, Saturday and Sunday to raise money for food parcels for needy families. Generally it gets people in the Christmas spirit.’
The tree has been sponsored by PWC, International Energy Group and Butterfield.
It is the focal point of the Rotary Club’s present-giving campaign, which encourages members of the public to provide a Christmas present for a deserving child to open on Christmas morning.
Mr Parish said most of the presents were distributed by agencies, so they rarely saw directly the benefit the presents had.
But sometimes if tags were returned late, the club delivers the gifts themselves.
‘The parents just have tears in their eyes,’ he said.
‘It makes all the difference to them as it means there is something to put under the tree.’
Tags for these gifts will be available from Creasey’s Toy Shop, Aladdin’s Cave, Guernsey Post, in Smith Street, Fletcher Sports in the Arcade, Co-op St Martin’s, NatWest St Sampson’s and High Street and Barclays High Street.
The present should be returned by 10 December to the places where the tag was taken from, or to Fletcher Sports.