If the council usually does an Easter egg hunt they should continue to do an Easter egg hunt. If councillors usually help then councillors should continue to help. If councillors want to advertise their involvement with it themselves they can do that, the council should not. Publicity should not reference councillors, statements for publicity should come from officers not councillors.
If you want examples of how high the bar is set, a town council near me gave out Easter eggs to school children with a picture of a town councillor who was standing in a local authority by-election for the same area on the eggs and the police said that it wasn't a breach. A couple of years ago, in my ward the local authority delivered a letter from the sitting councillors with their political party mentioned after their names saying that they were going to consult on traffic calming later in the year during all out local elections and that was deemed not to be a breach. Purdah is barely worth the paper it's written on.