Kirsty Belsham, 22, and Alex Wilson, 23, had become engaged just days before the crash on Runshaw Lane in Euxton on Thursday last week.
They left two children, Lacey May, five, and Tyler James, four.
Annie Burns and Michaela Beech, friends of Kirsty’s family, set up a fund-raising appeal to create a trust fund for the youngsters.
Yesterday they had reached 245 donations totalling £4,290.
Alex’s grandmother Elspbeth Wilson, with whom he lived in Farington Moss, near Leyland, said: “I’m just totally overwhelmed. I can’t thank these girls enough.”
The money will be made available to the children when they turn 18.
Michaela, 25, from Leyland, said: “They have helped us out in the past and obviously you can’t put a price on your parents, but hopefully this will help when they are older.”
Annie, 25, said: “It’s been amazing. Leyland is such a small place but everyone has come together. The whole town has been so supportive and joined in with us.”
The initial target has been increased from £2,000 to £5,000, but they will keep raising money once they pass that.
They raised £248 with football cards in Leyland pubs, have plans to hold fun days and are asking for other ideas.
Balshaw’s CE High School will donate money from its Lenten charity fortnight.
A statement on the school’s website said: “Kirsty was a former student at Balshaw’s and had recently been working in school.
“Our thoughts and prayers are with their families.”
To donate, go to www.gofundme.com/laceyandtyler.