We all tend to underestimate the mental capacity of our kids. Your little one's brain is like a sponge that can store huge amount of information. The brain of your 7 year-old child works very differently than how your brain works. Some things that are very difficult for us to memorize comes very easily to our kids and poems are one of them. Poems help children with sequential learning and understanding of many mathematical concepts.
What you need to know
Memory is a complex process and every child employs his own tactic to store memory in his brain. As a parent you will have to find out what works best for your child. It is not a one size that fits all and you might have to go through multiple trial and errors to hit the jackpot. Encourage your child to recite poems but try not to force. It should come naturally to him in play and not like a forced teaching.