Mochi is tricky for the extreme elderly, because (A) a lot of them don't have healthy teeth to bite them in pieces and (B) their throats tend to dry therefore making it more difficult for mochi to be swallowed down.
So when feeding elderlies, you are encouraged to cut mochi in tiny pieces so that even if they fail to chew them enough before swallowing, it will still leave a space to breath inside their throats. If they happen to swallow a big lump, vacume cleaners are a handy tool to pull it out.
I've never heard about taking extra care when feeding mochi to toddlers, but I suppose that (A) toddlers' throats are not as dry and (B) you take extra care anyway.
I think the tricky part about mochi is that the Japanese tend to expect elderlies to be used to mochi, while in reality they age and are not who they were yesterday. Meanwhile, you expect toddlers to be weak, so you cut everything in pieces and keep a good eye on them anyway.
One thing we are encouraged to keep in mind however are to avoid feeding "kon-nyaku jelly" to toddlers. Kon-nyaku jelly are tiny cup-shaped snacks that were invented in the recent decades. But unlike gelatine jelly, it doesn't melt in your mouth. It contains more fibers and therefore will not break up unless you chew them (which is the reason it's good for people trying to loose weight).
People tend to miss out on this fact, expecting it to be similar to gelatine jelly (which is also available in similar shapes), hence the warning. Also, these tiny snacks can be very attractive for toddlers when left in the cupboard.
I suppose it's all down to the balance of what you expect and what reality offers you.