Try to feed baby during take offs and landing if baby is not on pacifier (this can help to relieve some pressure from their ears).
If baby is with you, you’ll be able to bring liquid in (do note when come back, it may not be the same for individual airports/staffs). I make baby milk on board (ask FA for hot water) to top up my cold formula stash (baby prefer cold formula). I also had a few bottles of premade cold formula which I also asked FA to store in fridge for me.
Prepack baby formula in disposable milk powder bags.