This year I decided to take my elder two children (8 and 6) with me. We were going to travel up Thursday night, Expo Friday, and see what happens Saturday. We ended up just doing the Friday but man, it was incredible. They were so excited to see their cousins, see the cosplayers, play some games, and buy their own dice. I got my dice out a couple of weeks ago and we just played with them building towers, which then led into playing a wargame. From that moment the girls wanted their own dice, and I can't attend a convention like this without buying a set (ask me when I last used a D4 though...).
My eldest daughter signed up for a kids DnD session - loved it. We went to a stall where they gave out free D20s with a little snail body to rest them in. My girls are now hooked on dice. We spent quite a bit of time looking at various vendors and ended up deciding on one that was promoting a new RPG game that was crow themed. It was two sets for £10 so I bought one for me, one for each of them and one for my 3rd who immediately lost one when we gave it to him. The guy there also told the girls to pick up a free die from the basket of dice where you pick one for 50p if you want it. They were spoilt. This does mean I will have to now figure out a child-friendly RPG system to do little adventure with them.
In the evenings I played Terraforming Mars - it lasted a long time but was amazing. We barely built any green areas in the first 6 or 7 generations. It went on to 10 generations.
I was introduced to Kites and Pairs. Both fun, quick games. I want more like these.