The organisation, which was co-founded by former Emmerdale star Miller last year, will host the Raising Smiles Fundraising Weekend between November 23 and 25 as part of its continued efforts to help bereaved families.
Once Upon A Smile supports those who have lost a parent or child through long-term illness, with initiatives including respite breaks and help with bill payments.
Miller has recruited a number of familiar faces from the soap world as patrons, including EastEnders stars Matt Lapinskas and Tony Discipline, Hollyoaks returnee James Sutton and former Waterloo Road cast members Will Rush and Jack McMullen.
As part of the Raising Smiles weekend, the charity is encouraging people to secure new donations for the cause with personal fundraising - whether it be sponsored challenges, an event at school or work, packing bags at supermarkets, taking collections or putting an item up for auction.
With just under two weeks until the three-day event begins, those interested are advised to think about potential fundraising ideas.
Nearer the time, it will also be possible to sponsor participants via their individual Justgiving pages.
More information on Once Upon A Smile can be found on its official website, while any enquiries regarding the Raising Smiles weekend should be sent to the organisation's Twitter and Facebook pages.