Leicestershire County Council has written to parents as Covid cases double in a week.
Areas such as Blaby and Charnwood in particular have seen an increase in their rates of Coronavirus case rates.
The Delta variant, first discovered in India, has 'wiped out' the Kent strain according to the County's Director of Public Health Mike Sandys.
This variant is thought to be 40% more transmissible than previous variants.
The letter which is penned by Mr Sandys and Jane Moore, Director of Children's Services, asks parents to be sensible when arranging 'gatherings' such as birthday parties or sleepovers.
Children and young people seem to be driving the latest increase in cases.
Deaths and hospitalisations remain low and the number of cases are relatively small compared to figures from January. Yet the letter warns we could be in for a 'bumpy ride' if we do not take action now.