I quite agree. But correct me if I am wrong but the Base fare is a cheap fare that offers no "frills" such as pre-selected seating. To buy that "frill" you need to buy Base Plus. I do not believe Lan makes that difference based on safety, but rather offering you more options for more expensive fare. But if believe it to be, they do offer you that option. A few dollars more for your peace of mind, and safety of your child, may well be worth it.

Sitting beside a stranger is not a breach of child safety, unless there is some extenuating circumstance I am missing. I wonder too about your concern... maybe there is some other way to mitigate it whatever it is?