Why not make it twin size - then he can lay on part and have the rest come up over him and it would also be long enough for the years to come. When he grows more and doesn't take naps then his mother could use it for a lap cover while watching tv like I did so many years ago. My kids used their quilts that were just quilted material and bound (by my mother) until they were absolutly threadbear because there were big enough for growth.