If your child is currently very young, you likely have 15-18 years until a professional degree, which gives equity-heavy investments (SIPs into diversified mutual funds) plenty of time to work through market cycles and benefit from compounding, with the allocation gradually shifting toward safer instruments as the goal approaches.
If your child is already in their early teens, with 4-8 years to go, the time horizon is shorter, and a more balanced mix between equity and debt (PPF, FDs) becomes more appropriate, since there's meaningfully less time to recover from a market downturn right before the money is needed.
It's worth periodically revisiting your estimated future cost as your child grows and their actual academic path becomes clearer — an engineering degree, a medical degree, and study abroad all carry very different cost trajectories, and a plan built on a rough guess at birth benefits from being refined as more information becomes available over the years.