They had no problem attending a tennis match in Paris not so long ago without the children, so a sick child would not really be an excuse for missing the most important event of the year. So her not being mentioned is strange, if she is pregnant and they do not want to announce it already they should have said sth like "sorry Claire can't attend because she has a bad cold or sth similar". We will see if this is just another blunder of their new press team or if she really is missing. Felix is listed for today's reception with his parents, so we will see if he attends alone, with Claire or if none of them attends. Having Felix attend 3 days of the National Day events makes me think that there is nothing wrong with the children or with Claire's health, otherwise he wouldn't have been listed for 3 days of the event, especially since even Gui and Linus are not listed for today's event.
Not that a press team blunder is a good thing, but hopefully that's it because it'd be a real disappointment for her not to show at all (though not unusual for the Lux kids/spouses).