Help! Do you know symmetrical opening lines?

I train my 4 year-old son.

My son always wants to have black and he duplicates my (white’s) moves in the opening. ex. 1.d4 d5 2. Nf3 Nf6 3.e3 e6 …..

So, I am thinking to teach an opening which has "symmetrical position" to him.

Do you know such opening line(s) which has symmetrical position, say up to at least 10 moves?