Is there a possibility that small vsd become a large vsd as the child grows?

Generally Not. In general, vsds do not significantly grow larger as the child does. In fact, it is more common for them to stay the same size or potentially even become smaller.
Yes and No. If it is a perimembranous vsd. If it is muscular it will likely become smaller and eventually will close. Follow up exams are needed either way.
No. Ventricular septal defects (vsds) may become smaller with age, but do not enlarge as a child grows.