Many modern neopagen sects seem to think that they were relatively open sexually and that they used ritualistic sex in their religious practices. Is this accurate? That seems like a dangerous proposition in a pre birth control world.
I'm not a trained historian, but questions about druids and Celts show up here and reportedly can be difficult to answer. Below I've linked some comments by flaired historians in prior threads that get into these issues, which you may find interesting reads.
On the sparseness of any sort of useful sources about the druids:
from /u/depanneur https://www.reddit.com/r/AskHistorians/comments/4imvkm/were_there_any_barbarian_philosophers_in_the/d2zw0uo/
from /u/TarvosTrigaranus https://www.reddit.com/r/AskHistorians/comments/7c2di6/a_history_teacher_of_mine_mentioned_how_the_druid/dpn31gy/
Two from /u/Tiako https://www.reddit.com/r/AskHistorians/comments/2r4ehg/what_do_we_actually_know_about_ancient_druidism/cncekmb/
And on the problematic nature of the term Celtic:
from /u/itsallfolklore https://www.reddit.com/r/AskHistorians/comments/3sgo4u/how_should_we_best_understand_the_celts_were_they/cwx576g/
And these 3 from /u/Miles_Sine_Castrum https://www.reddit.com/r/AskHistorians/comments/4ehhwc/what_caused_the_celtic_expansions_across_europe/d20gvy4/
My thanks to mod /u/cleopatra_philopater for patiently instructing me on how to bring this comment into line as a permissible non-historian reply.