Mike,
First of all, that's a real nice piece of equipment, anyone should be proud to have it installed in their house.
However, I think your suspicion's are valid. My little Becca is really an escape artist, and I'm sure your little one, could get through those spaces.
Here's a temporary (and removable) addition you might make...
There's some metal screen they call "
Hardware Cloth".
It comes in 24" widths, and you can buy a piece which
is 51" (the width of your gate) long.
Then, just use some string or a few of those wire ties like comes
on a Bread Loaf, to block the lower section until he grows enough
where he can't get his shoulders through the openings.
Then just take it down, and wrap it around one of your plants
to keep the Squirrels out
