Andy, I've not looked for construction related presentations in this area but a year or so ago I did stumble across the Virtual Quarry site - http://www.virtualquarry.co.uk/t_trespass.htm This is produced by the Mineral Products Association. My link above takes you to the Teenage Trespass area of the site with teachers materials and briefings. Obviously you're not going to be able to use this as it stands but it might help with a few ideas.

I advise that you keep it short, sharp/crisp and to the point and personal to them otherwise you will lose them in the first minute at the extreme I would go for 10 mins only and forget adding in the law and all that type of thing as kids are just not interested

Andy We do quite a lot of talks. Agree with most comments 10-15 minutes is more than enough 5-11 year olds you can have more fun (hazard spotting, PPE dressing up, etc) I have a powerpoint we use (all pictures) to base your talk around. There is an excellent 6 minute video/DVD called gameover produced by HSE if you can get hold of it (aimed at 7-11 year olds) 11-16 year olds different kettle of fish. Feedback from a couple of headmasters was to tell them exactly what the hazards are and how they could be hurt (fatal/major injuries) standing on a nails, breaking your back falling off a scaffold, getting run over by a delivery lorry, buried in a trench etc. Statistics show its mainly young males that venture onto construction sites so need to emphasise it. There are a few case studies of youngsters being killed so can refer to them. Tell them a bit about the project too, how you will be setting up site, deliveries, logistics etc. I have a previous presentation (1 page of notes) I could email you Good luck