Take a firm stand:
First of all you will have to make them realise that you are completely ready to supervise your kid. You can talk to them and pass on your reservations. However, you should not be harsh and rude rather request them politely to follow the rules.
Support your partner:
You and your spouse should be on the same page as this united front can really help them to understand. If anyone of you is showing disagreement on some point then it will give them impression that you need guidance to raise your child properly.
Examples from their own life:
Make them realise that you will learn to prepare the toddler for practical life. Remind them of their period when they raised you without having a prior experience. Tell them that you appreciate their concern but you are in charge now.
Remember, old people are just like kids. They are stubborn and persistent but still lovable. Whatever they do is the result of their concern and love to you. All you need is to tell them how they can be helpful in raising your child. Set some rules and ask them to follow as they are for their own good.
This exercise does not mean that you should keep them away from your child. The recent studies show that grandparents are key part of your kid’s life so you should stay connected to them. Appreciate them for showing concern and give them the impression that you value their suggestions.
Understand their nature:
All you need is to understand their psyche. They are your parents and it has become their second nature to guide you in every matter of life.