What do the bots do? How do larger size groups differ from smaller ones that effect their suitability/appropriateness?
WhatsApp isn't filtered; it's fully permitted even by Meshimer, if requested, the most stringent of the filtering companies. Telegram is disallowed and won't be approved even if requested.
Bots are basically websites... You can connect to a bot and get a lot of inappropriate content (and unfortunately there are probably more inappropriate bots than appropriate ones.) The bots are public and are searchable.
Bigger groups (and channels) also make it more of a content delivery system than a social group.
Also with WhatsApp its much harder to remain anonymous.