I think the secret diary is too old, many children are barely be able to read or write in reception, colouring sets, nice stationary in a pencil case, stencils or spirograph better for that age group.
Plus plus probably wouldn't appeal to many of that age either? My DD got into those when she was 10.
TK Max was always my go to place to stock up. Board games are something my children loved so I'm surprised you don't think they would be popular