Phoenix 10 is the 44-acre former James Bridge Copper Works in Walsall, which is creating 1,000 jobs for the region.
Earthworks are currently underway with workmen filling in mineshafts and doing other remediation works
Simon Raiye, Director at HBD, said: "It’s important to us, with so many children off school for the summer holidays, to reinforce the importance of safety around any active development site.
"We’ve sent letters to all our neighbours and our security team will remain in place 24/7. We will continue to keep the community updated as works progress and our project website, phoenix10walsall, remains live for people to visit for updates."
He added: "This site is the largest undeveloped brownfield site in the Black Country and has huge regeneration potential. Having been derelict for more than 20 years.
"It’s an exciting scheme that will add massive value to the local community in Walsall and support a thriving regional economy."