Tonight at 5.15pm, CBBC will start to show the last remaining episodes of The Sarah Jane Adventures, filmed before Elisabeth Sladen died from cancer at the age of 63 earlier this year. Beyond the obvious grief of the occasion, it is also a sad loss for children's television.

Commissioned in 2006 as a spin-off from Doctor Who – more specifically, the series two episode School Reunion – the alien adventures of journalist and former companion, Sarah Jane Smith were something special. With her adopted son Luke, friends Clyde and Rani, and robot dog K9, Sarah Jane guided children through a drama built upon adult ideas, with storylines that were smart, imaginative and never patronised the show's audience.

"We never really, in writing it, thought of The Sarah Jane Adventures as a kids' show" explains lead writer and co-producer, Phil Ford. "Our thinking was of an adult action-adventure show which was merely suitable for children. We've never shied away from difficult subjects."

Throughout its five series run, TSJA has tackled issues such as Alzheimer's – in the Eye of the Gorgon no cure is miraculously discovered, nor is the subject matter simply glossed over. "We've always tried to be emotionally truthful", says Ford. Such ambition has seen the show have its script ideas turned down for being too similar to upcoming episodes of Doctor Who, despite having only a fraction of its budget. Indeed, in 2009, Russell T Davies revealed the show was nearly cancelled three times due to the lack of money invested in children's television.

Even so, The Sarah Jane Adventures has powered on – occupying a unique place in the Whoniverse. In terms of how it has been viewed in the franchise's canon, it has held a far more credible position than Torchwood – whose world of sex, violence and immortal paedophiles jars. Steven Moffat even confirmed as much earlier this year when he said the Doctor would never appear in Torchwood because "it's not really a children's show". However, David Tennant and Matt Smith have appeared in TSJA .

But at the centre of the show has always been Elisabeth Sladen. It's a poignant thought that for certain kids, she was their Doctor. Although, admittedly, rather easier to relate to than the God-like hyperbole of The Oncoming Storm himself.

Which is a pleasant irony, given that the original concept for the CBBC spin-off – vetoed by Davies – was a young Doctor growing up on Gallifrey. "I wonder if the BBC would ever have considered commissioning a series about a 60-year-old woman in the lead of a kids' show if there had not been that Doctor Who connection?" Ford asks himself. "I'm sure they wouldn't. Then again, of all the companions the Doctor had over the years, there was something special about Sarah Jane. She wasn't so much a screaming sidekick – she was a character in her own right. She wasn't there just to scream at the aliens, she was there to take the fight to them. I think that's why the character has had such longevity. That's the tragedy of this, really: she still had so much more to give."

Even though these three new stories (told across six episodes) are rightfully intended as a celebration of Sladen, they're also inescapably sad. Was it the right decision to show them? "Obviously we have to consider the feelings of the family [who gave permission for the episodes to be shown] and in many ways, it is a confrontation with death for some kids," Ford says.

"But they're great episodes and I think it's what she would have wanted. She knew how important that character was to the kids who watch it, and I think the last thing she would have wanted was to have three great stories which were never shown."

"The downside, beyond words, is that Lis isn't here to enjoy it herself. Because she's truly, truly magnificent in them."