Hi okaay!
So I watched this movie so so long ago and I've been looking for it for years!
Its basically all I can remember is

Opening scene of all these kids on bikes handing out newspapers
And 2 of the kids are brother and sisters.
I remember the brother and sister brushing their teeth in the bathroom and the girl then sneezes and the boy says something like
"Your the princess" or "your the missing princess"
Not entirely sure.
I realise its not much to go on but I'm desperate so please please help meeeee
Key word is "princess"
Thanks for your help xx

I think you're looking for Clubhouse Detectives Search for the Lost Princess. I can only find this clip - and for some reason there is no sound! There is a toothbrush scene at 26 seconds, then a sneezing scene at 1min.
Clubhouse Detectives: Search of a Lost Princess SD trailer on Vimeo

Amazon.com: The Clubhouse Detectives - Search of a Lost Princess: Brittany Armstrong, Jonathan Cronin, Susan Duerden, Hilary Hughes, Michael Glauser, Eric Hendershot: Movies & TV