yeah it's not great, they would need grit to digest that and like you say can be quite big for chicks. I prefer ready made chick crumbs. What you have would be great as a treat once or twice a week but you would need to add grit and finding grit for chicks is challenging too - I've bought pidgeon grit as it is smaller than chicken grit for this purpose, not sure what others do tbh.
It's better than nothing for now, if you have a mixer you could try crushing it down a bit smaller but my main concern like said would be grit.
Get something more suitable as soon as you can, I'm sure the shop will have had several differnt varieties and although this one has been cut down for chicks they are still considered more of an occasional treat than a specially formulated chick feed.