You just need to kick puddles on them to inflate them, the one over on the far left doesn’t have a puddle near it but if you have the goose you can run over to the shrimp and he should get a black cloud meaning he wants fed feed him and then stay near and wait for him to poop and then kick the poop on the shrimp.
Heh I did this on the first visit to the harbour with no water balloons as ragnarok says you can always go back once you have the water balloons and just throw them.