In the end it's completely up to you guys no one can tell you want you should and shouldn't do. It might pay to explain that some children believe in Santa and not to spoil their fun....but in the end all kids find out!
True, all children do end up finding out, but you don't want to spoil it for them until they are ready "not to believe"

I too, cannot remember being upset at all, and it was another child who spoilt it for me who's parents told her from kinder that Santa was not true.

Like Blue_hebe said, in the end, it is your decision what you want to tell your kids.