Totally agree with krysalyss and was thinking the same thing. There actually won't be a lot of time to sit around and chat iykwim? There will be the odd one or two line convo all day I bet!

Either OH or a Nan would be my options - if the hosts are saying all family, older siblings etc are welcome they will not mind in the slightest that a Nan is coming. Having said that it would depend on how important the workshop was to me/work etc as OP mentioned.

Good luck!