I've taken a look at La Baume's website. The campsite is well outside of the town of Frejus, so it looks like you'll have to find a taxi for the last part of the journey.
The Nice Airport website states that S.V.A. run a direct bus service to Frejus, daily at 0900, 1230, 1545 and 1930. The fare is 21.20 euros for adults and 17.00 euros for children (4 to 14 years). There are no details of the return service but you could try e-mailing S.V.A. at
[email protected] . Alternatively, phone 00 33 49 49 59 51 6.
It might be cheaper to take the train. There's a frequent bus service (daytime only) from the Airport to the rail station. (20 minute journey. Fare 4 euros each). If at least one of your children is between 4 and 11, you can get the Child Discovery Plus fare. This gives a total figure, for all 4 people, for the return journey of just �36. (That figure is quoted in Sterling because it was obtained from SNCF's UK website:
http://www.sncf.co.uk
Note that you have to select the journey as from Nice to 'Any Other Station' and then amend the destination to Frejus on the next page).
The taxi fare to Frejus, from Nice Airport, is quoted as being in the range 113 to 154 euros from 0700 to 1900. Night fares (between 1900 and 0700) are quoted in the range 134 to 170 euros.
Main source:
http://www.nice.aeroport.fr/acces_stationnemen t_en/plan/default.asp
Chris