A couple weeks ago we carried on some electronic toys...yahtzee game, etc. We didn't have any problems in security. In fact, the screener commented about his hot wheel cars as the bag went through.
They did say, though, that at SWA the computer picks out certain itineraries and they then do complete searches on those individuals. If you were the lucky one then it could take you quite some time to get through.
I thought it was nice of SWA, though, if that happens to you, at least on our last flight, they let those individuals board in the pre-board instead of waiting to board with their number.
If your kids are younger and will be in the carseat the whole time, we found that we could put a small blanket from the pocket on the back of the seat to under the carseat to make kinda like a "catcher" thing. That way the toys didn't go all the way down to the floor. Just an idea incase you have little ones. We always bought a separate seat so he was never on our laps.