You should be fine. When my wife and I came over (which was before Tier 4 was released), we both had access to the NHS. A colleague of mine is brought her children over as well (under Tier 4), and they've legal access to the NHS. The way that I've interpreted the rules is basically that anyone who's legally allowed to stay in the UK for more than 6 months has a legal right to access the NHS. That means students, spouses/partners and children who are staying longer than 6 months on a proper visa.