When you say 2 metres from the creche, I take it you mean 2 metres from the playground? The purpose of the hoarding will be to provide a boundary to the site - it is never intended to act as a physical barrier for out of control trucks, even at a few km/hr it couldn't do that. Instead you have to think of the drivers operating their trucks on the construction site in a safe manner, assessing their stopping distance by taking the driving conditions into account and being able to see the site boundary because of the hoarding - much like the rest of us do every time we park in a public car park.
Is this a large construction project? On construction projects which will take more than 30 days or more than 500 person day or where there is more than one contractor involved, there is a requirement under the Construction Regulations 2013 to appoint a PSDP (Project Supervisor Design Process) and a PSCS (Project Supervisor Construction Stage). These will be involved in preparing safety plans including a traffic management plan as part of the overall planning and phasing of the job. In preparing plans, they should consider not only the activities happening on site but also those in the immediate proximity - so in this case the importance of maintaining a secure boundary between the creche and the site would be particularly relevant as JPD points out.
The OP hasn't elaborated on their connection to the project. Reputable construction companies will employ or engage safety advisors to work with the PSDP and PSCS and such companies are normally more than happy to discuss safety matters with neighbours in the interest of good working relationships. Obviously the earlier that contact can be made with the contractor the better from the point of view of their understanding of the concerns of their neighbours and to give the builders an opportunity to explain the method statements and safety plans that they are putting in place.
