I don't think you're giving employees enough credit here. They can remember the current toy. They really can.
I remember when the original Cars was still in the advertising mode and we were waiting ever so patiently for the movie, McD's had the Cars characters...tons of them, and they switched every few weeks all summer long.
I was forever calling and stopping by different McD's because my kid was so super obsessed with Cars already, and the employees never had any issue knowing exactly what the current characters were AND if they had any older ones hanging around, too.
(Sure, they may sometimes say the wrong thing once and again, but that's true of anything.
)
Plus, it saves them some time, too. Because inevitably if they say "Boy or Girl?", there will absolutely be people who will then ask what the current toys are. And then they need to say "Hot Wheel" or "Barbie", anyway.
By the way, saw that they are bringing back all these nostalgic Happy Meal toys, so I bet they'll be getting people calling and stopping by trying to get them all just like we did back in the Cars days.
And along that same line of thought, I bet most kids and parents know exactly what toy they want before they even place their order, so they can just order the "Hot Wheel" happy meal right off the bat and avoid the question entirely.