The Society for Popular Astronomy holds quarterly meetings, the next one is on the 24th April, the main speaker is Prof Gerry Gilmore, Cambridge IoA, with “The Faintest Galaxies: Steps toward Dark Matter”. Members and friends are welcome from 2-5pm at the Khalili Lecture Theatre, SOAS London. Directions and videos of past meetings available at that link.
For those in America, the largest astronomy show will be held on the 17th-18th of April in New York. The North Earth Astronomy Forum will be at the Rocklands Community College, Suffern, New York. Children are free (to go in, I assume, not a gift for going along).
Meanwhile, back in Blighty, if you’re looking for a planetarium near you, the British Association of Planetaria have a website with a planetarium finder.