Okay kiddo! In Christianity, we believe that Mary (the mother of Jesus) is very special and important. We call her the Theotokos, which means "God-bearer."
Now, intercession means asking someone to help us or speak to someone else for us. So when we talk about the intercession of the Theotokos, we mean asking Mary to pray for us or to speak to God on our behalf.
Why do we ask Mary to do this? Well, first of all, she is Jesus' mother, so she has a special relationship with Him. We believe that she is with Him in heaven, and that she can hear our prayers and requests.
But even more importantly, we believe that Mary loves us and wants to help us. We think she is a great example of someone who always obeyed God and did the right thing, so we ask her to pray for us and help us to be like her.
So when we say "intercession of the Theotokos," we are talking about asking Mary to be our friend and help us to be better Christians.