I was to take the DC to some of this next Sunday (ages 8 and 10). But I'm overwhelmed with all the choice (and the rather unhelpful filters). I thought about 10, Downing Street, but there's a lottery for that, so it seems unlikely we'd get that. And some of the other iconic buildings I thought of (like The Gherkin) seem to have rather stressful arrangements like being in groups, strictly timed, with full body scans!
Can anyone recommend any fun/exciting/amazing places likely to enthuse this kind of age of kids but that don't have stringent security or huge crowds? Central-ish boroughs preferred, unless there are a couple together in an outer borough.