It can be difficult to know what to say to kids about the Trinity. Try this next time:
Can anyone tell me why they think the love we give (and receive from others) is imperfect?
I reckon it is because human love is always given with a good splash of our own needs mixed in. And our needs - most often legitimate - shape our love so that it is not actually for the other person. It is for me as well. No parent can love their child perfectly, just as no child can love their parent perfectly. So too with our friends and anyone else for that matter.
But not so with God. God is love already. God doesn't need us to have someone to love, or need us to have someone to love God back. God is love. A communion/community of love. That is what the language of Father and Son, and their mutual love of the Holy Spirit, is meant to signify. God doesn't need us. But this is exactly why God loves us. It is for us, not mixed in with God's own neediness. (God is needless in this sense, not in a frigid sort of cold and distant sense.)
This is why it is so important to let God be God, and ourselves and everyone to be less than perfect. So many people bear a grudge against a parent or child or friend or someone they hardly know because that person was human, that is, couldn't love them perfectly. But that is to ask them to be who they cannot be. Why ask people to be who they are not? What they are not?
God Alone is Good
You can Trust God
Further Thoughts on Transcendence