we had to re prune to lower what ought to be a new "y" as the tree got
pretty damaged... the whole thing is pretty young, only 5-6 years,

You never want a y shaped fork on a tree. This is weak & will break in a storm.
Always prune so there is one main trunk & the branches are at right angles.

there is now aphids and the leaves look a little sick, I am assuming that
the tree got stressed and is not happy.

Feed it. You can get fertilizer sticks that you pound into the ground. Spray
for the aphids.

there are ants herding the aphids too

Not much you can do outdoors, as the insecticides for ants are very potent. If
you see anthills at a few noticeable locations, you can try using ant traps if
you can make sure the kids don't touch them. You can probably keep the ants &
aphids at bay by repeated spraying with a strong jet of water, if it doesn't
damage the tree.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)