I should stress that many of the Texas FLDS members may still be in huge legal trouble, despite the conclusion that the raid was illegal (and likely unconstitutional) as to many of the children.

1. Rape / Statutory Rape Prosecutions: Most obviously, if indeed some girls (1) were physically forced into marriage or sex, or (2) had sex before age 17 with someone to whom they weren't legally married (whether there was no marriage ceremony or there was such a ceremony but it wasn't properly registered with the state for various reasons, such as the fact that it was an unlawful polygamous marriage), the people who had sex with them would be guilty of rape or statutory rape.

2. Prosecutions for Aiding and Abetting Rape / Statutory Rape: Criminal liability could also extend to those who sufficiently aided in the conduct, even if the aid consisted solely of encouraging the behavior (by which I mean encouraging the specific marriage, and not just teaching in the abstract that early marriage was good). This could include the girls' parents, religious leaders, or even friends and relatives who actively encouraged the conduct. The boundary between being a mere nonobjecting bystander (not criminal) and an active participant (criminal) is unfortunately sometimes quite vague. I suspect that celebrating the wedding with the couple or giving a wedding present wouldn't qualify as aiding and abetting, but even that's not completely obvious (see the English case Wilcox v. Jeffery, which some criminal law scholars see as being relevant to American law).

3. Bigamy (and Aiding and Abetting Bigamy): I suspect that the Texas bigamy statute -- which applies when a person "(A) purports to marry or does marry a person other than his spouse ... under circumstances that would, but for the actor's prior marriage, constitute a marriage; or (B) lives with a person other than his spouse in this state under the appearance of being married" -- wouldn't be interpreted as covering ceremonies that the parties understand not to be legal marriages. Clause A wouldn't apply, I think, if no marriage license were applied for, since without such a license the circumstances wouldn't constitute a legal marriage (Texas common-law marriage rules don't apply when one party is already married). Clause B is harder to figure out, but my guess is that this requires representation to others that one is legally married.

The Utah Supreme Court recently interpreted Utah bigamy law more broadly, to cover second marriages even when they aren't claimed to be legally valid marriages; but Utah law said simply that, "A person is guilty of bigamy when, knowing he has a husband or wife or knowing the other person has a husband or wife, the person purports to marry another person or cohabits with another person," without the "under circumstances" language.

4. Regular Proceedings to Remove Children from Parental Custody: Naturally, if there is sufficient evidence of some past abuse of children, of imminent future abuse, or of parents' idly standing by when the children were abused by others, those children could be removed from parental custody, even in the absence of a criminal prosecution of the parents. It's just that this would have to be done through the normal procedures, at which specific evidence of abuse or likely future abuse of those children would have to be shown.