Ok this can be a little tricky with kids, as they are going to want “toys”. So go ahead and get them 1 toy but then maybe a Bank or Clock something that can be put out and not lost, or thrown away.
I have found the best souvenirs to be items I will continue to use once I get back home, scarves, gloves, shoes, wallet. Since I don’t wear a lot of jewelry, I stopped buying it around the second trip, because it just sits in my jewelry box collection dust. I use the wallet from Venice everyday, I used the scarf and gloves from Paris when it is cold, I was using the shoes from Rome for work. I purchased a Little change purse in Marrakesh and I wish I would have got more for gifts.
The main thing we do is get pictures from our trips. We found that we can find scenes from where we have been. We do have to take them off the frame or wood they are stretched on to get them in the suitcase, and then we get them reframed when we get home.
You are supporting local artists and you get a very personalized item (we usually get a picture of a specific place that we visited) that can be nicely displayed. They come in water colors, oil paints, pencil sketches, all sorts of things. Here are just a few of ours for example.