I am all for knowledge for knowledge's sake, but encourage them to consider employability at the other end.
I know that this is not quite what you asked, but I did work experience in archaeology whilst at school at decided against an archaeology degree which I was previously set on on the basis of the practical experience, and also the feedback of those working there. Most of them did not have archaeology degrees, those that did were in the absolute minority of their cohorts who had jobs, let alone a relevant job, and most of the work was either absolute guess work, or it was running around trying to deal with complete f* ups where construction workers had drilled into archaeological sites without doing a survey and they were trying to preserve stuff. I know we are 20 years on, but my understanding is that there has not been a sea-change. A lot of the "work" in the field in terms of digs etc they can get volunteers to do. Much like conservation, there are far fewer paid jobs than the number of students studying it, and the students studying it are not necessarily in the best position to get the paid jobs as new graduates.
It's not like Time Team. I had this romantic idea that I'd be canoeing up the amazon to reach digs and finding amazing stuff. It's not like that. Carbon dating is not used for anything other than the most exciting finds because it's expensive. It's mainly washing and labelling bits of generic Roman pot. It's not routinely digging up exciting skeletons, putting them back together and carbon dating them. And the people doing that sort of fun stuff often have considerable experience in medicine/dentistry/pathology/human biology first and have then gone down that road, not archaeology degrees - at least this was the case when I was considering options, and frankly it makes sense!
I would encourage them to get some practical experience and advice before heading down that path. Depending on the type of archaeology they want to do, it may be that a really good quality science degree, or for example an art degree (for example, if they are interested in the restoration of ancient artifacts - I met an amazing woman who restores pottery and basically attempts to recreate the original from the pieces, which is painstaking work), or something IT/technical design based which teaches really high level landscape and computer modelling, alongside relevant volunteer work experience (join the Young Archeologists Club and go to monthly meetings as a starting point) will actually make them more employable in the field if they are prepared to play the "long game".
Failing that, consider looking at places that will do a dual degree which make gives them either the raw science, raw art or raw IT skills which might provide more career options on graduation.