That's a great idea! I like their small pots that fit in top of a canning jar - to allow people to carry vegetables and humus.

Those glass jars are, however, heavy. I'm already transporting 15 kg of child, plus stuff. Is the additional weight of a heavy glass drink container worth it?

(I also like that these are not "valved" cups, but are "free flow". "Valved" or "no spill" drinking cups for children can cause ear problems.)