This is a minor incident and I'm not at all angry or upset, and I understand how hard the PTA works to put on events like the Christmas Fair.
In the interests of full disclosure, I went to the PTA meetings, Christmas Fair planning meeting, helped send letters to local businesses about the fair, helped design a game stall, purchased prizes for the stall, volunteered for half an hour to run the stall and volunteered for another half hour in Santa's Grotto, taking tickets and ushering families through to see Santa.
When my relief at the grotto arrived (call her Betty - she's the mum of a child in DC2's class and also a neighbour, who I have known for several years to chat at preschool or school gates with) a group of children I didn't know (not Betty's kids) came in with her, who I assumed were there to see Santa. I explained which presents were for preschoolers and which for older children as quickly and discretely as possible so I didn't spoil anything for them, and went on my way.
A few minutes later, I took my children in to see Santa. They loved it, but I was surprised to see the kids who had come in with Betty still in there. I realised then that Betty must be babysitting and had brought them along to watch.
I realised quite quickly that Betty was handing the gifts meant for preschoolers to Santa, for my DC1 (8) and DC2 (4). I pointed this out to her as discretely as I could - there were plenty of the gifts meant for school age children left. Instead of correcting the mistake, she kind of rolled her eyes at me, and thanked me for pointing it out, but didn't swap the gifts in her hands for the correct ones and handed them to Santa.
I didn't complain any further, but when we got out had a chat with my children to manage their expectations about what was in the gift. They were disappointed but not upset.
Was I being unreasonable to message the PTA chair to let her know the mix-up happened, and to ask how it can be avoided in future?
The gift for school age children would not be suitable for under 3 year olds as it has small parts and would be a choking risk.