Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
toc sach » hoc sach, doc sach, thuoc sach
van cac » van hac, van cau, van bac
ty nang » ky nang, ty xang, ty hang
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
bo van » vo van, do van, ho van
so van » su van, vo van
vi cua » vai cua, di cua
o hoi » co hoi, o hoc, o hai

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) OR (toc sach)) ty nang o hoi. hieu van cac ((bo van) or (so van)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ty nang o hoi. hieu van cac ((bo van) OR (so van)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) ty nang o hoi. hieu van cac ((bo van) or (so van)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) ty nang o hoi. hieu van cac ((bo van) or (so van)) hanh vi cua tre*.