I believe his spirit is in Heaven now with Jesus, but I don't know much (I don't think anyone does) about what happens to baby spirits in Heaven. Does he grow? Can a spirit grow? Will his resurrected body be a baby still? Has he been cared for and mothered by heavenly beings? It's made me think about Heaven so much more than I would otherwise! But I'm settled knowing that Matthias is in perfect peace, fullness of joy, and without any sadness or pain. He's the happiest little heavenly spirit that he could possibly be. (Sweet boy! I'm so glad you are There, but I miss you so much!) I'm pretty sure he'll know me as his mother and I'll know him as my child when I see him again.
In the mean time, I remember the very, very brief time I had with him. I remember the pain and shock of letting him go. I am thankful for the healing God has brought in our lives. And I rest in the sure and steadfast Hope we have in Christ!
"Therefore you too have grief now;
but I will see you again, and your heart will rejoice,
and no one will take your joy away from you."