Jesus, OP, judgemental, uptight and passive-aggressive much? And thank you for educating us on what should, according to you, be an occasion worthy of legitimately distracting a toddler's parent's attention away from your conversation, and the rude impression we may 'inadvertently' be giving should we stop our exclusive focus on you for anything short of a two-year-old teetering on a seventh-floor window ledge..
As others have said, once you have a child, biology dictates that you internalise his/her needs as a priority, and by the time they are toddlers, you have a finely-tuned sense of what you have to do to stave off a tantrum, prevent a toilet-training accident, or do whatever is needed to manage to have a conversation with a friend.
You think they are being rude to break off attention to offer a biscuit, but from their point of view, they're trying to create an environment where they can keep talking to a valued friend. Maybe even especially a friend without children, who is a link with their childfree life. They would probably much prefer to be able to see you without their toddler present, where they have to divide their attention between you and providing distractions, but it's not always possible.
Look, I'm not without sympathy, because I remember when my closest friend had her first child, and I expected everything would go on as before, but of course her attention was focused on her son, she was distracted, and I did leave her flat repeatedly wondering whether she'd even registered my presence. But I was a grown-up. And I know now what she couldn't say at the time, that she was unhappy, struggling with motherhood, and isolated, and desperately depended on our conversations as a lifeline to our friendship, even if I found them unsatisfactory and felt sidelined and downgraded.