Yes, they should leave en masse and have their offspring join the scouts instead.
The scouts have always welcomed people of all genders.
" At Scouts, we welcome people of all genders. We’re the largest mixed-gender youth organisation in the UK.
Girls and women have been in Scouts since the beginning. We’ve always had female volunteers. In 1909, there were around 6,000 girls in Scouts across the UK. "
Besides, it makes complete sense not to have them in a regressive organisation which reinforces dated gender stereotypes.
https://www.scouts.org.uk/volunteers/equity-diversity-and-inclusion/girls-and-women/