Happy for the suggestions so far, especially the idea of old electronics to take apart!
I love toy recommendations that come with a parental endorsement. I love lists too, but I get a little lost with them (I want to get everything recommended).
Speaking of parental endorsements, do any of your kids have a Rokenbok set and if so, do they like them? They look great, but I'm wondering whether they worth investing in considering that we already have tons of Lego?
And I also have recommendations: Our boys love ThinkFun logic and brainteaser games - Rush Hour, River Crossing, Shape by Shape, Hoppers. The SmartGames games are also great (Camelot Jr., Camouflage North Pole, IQ Twist, etc.). They're great because they're individual games, so they can actually play quietly. We often bring one or two out when things get a little too crazy around the house, and it works wonders.
And to your point on charitable gift giving indigo, I love that as well. We do a fair bit of volunteering and always involve our kids, and we also want to do something special at Christmas. One thing I've done with friends in the past was to make Christmas stockings for the homeless - we stuff new socks with things like deodorant, small sized shampoo bottles, chocolates, etc. We might repeat that one this year if there's still an organization that delivers them.
