Bracknell Forest councillors controversially voted in favour of the plans last month, which would also result in new primary, secondary and special needs schools plus a football stadium for Bracknell Town FC being built on the land.
However, youngsters who want to save the site gathered with their parents at the Binfield golf club last Thursday morning.
The children took part in a craft session as well as penning their thoughts to Mr Cameron, with the letters due to be sent later this week.
Laura Hogevold, from Binfield Village Protection Society, helped organise the event during half term.
She said: “The children were really creative, it was lovely to see. There was lots of glue and sticky paper. We’ve got a few letters we’re going to send off.”
Mrs Hogevold said the event – which raised about £165 in donations for the campaign to save Blue Mountain – showed people will not give up on preserving the site.
She said: “It was a great opportunity for a lot of parents to ask what is happening and we explained our position – we’re looking at our legal options and other options.
“We’ve got a really good team of people together assisting us, from people all round Binfield.
“We’re telling people to keep coming here to Blue Mountain to raise awareness of how popular it is. The function room was set up beautifully and the staff were very welcoming to all the children and families.”
Blue Mountain golf course had been subject to a legal covenant – introduced in 1991 – protecting it from development for 125 years. However, councillors voted to remove it at a heated meeting last month.