The two principal attractions on the Clyde, the Riverside Museum and the Glasgow Science Centre, are family-friendly affairs that could absorb children (and adults) for several hours each, particularly the latter. It's under a mile's walk between them via the Clydeside Distillery.
The Southside's attractions, several of which are architecturally notable buildings, are widely spread out, so time planning your route will be well spent. Some attractions are accessible via the subway; others are better reached by train or bus. The famous Burrell Collection is due to reopen in 2020; aim to spend at least half a day there.