TOTW is not all that large of a kibble, I'm surprised your little one can't eat it. Lots of 5lb and under Yorkies eat Acana and Orijen on here which is bigger than TOTW. I do know one member uses a nutcracker to make the kibble smaller (our spoiled dogs around here!
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I wouldn't personally recommend foods like Eukanuba and Royal Canin, as I find TOTW to be far superior to them, so it would kind of be a "downgrade", IMO. The dog food brand Fromm has really small kibble! Atleast the "Surf and Turf" variety did. Wellness has a small bites formula as well.