Rather amusing to read that some posters are still claiming that SF is the magic answer to this. The opportunity for any targeted operation was lost over three weeks ago. These children are now dispersed over a very wide area split into small groups. What are SF going to do? Wander through a forest bigger than Wales and hope they bump into a few?
The only way to find them now is through aerial reconnaissance and humint, and negotiate their release. Unfortunately as already posted the NAF is corrupt and feckless and The Nigerian intelligence service (SSS) is no better. Boko Haram have penetrated it far more effectively than they have penetrated Boko Haram.
Probably it will be the French who sort this out. They have aerial reconnaissance attitudes in place in N'Djamena and unlike us, they have developed a reasonable humint network in NE Nigeria and Cameroon as a result of several of their nationals having been kidnapped up there (a family of seven, then a priest) and spending a lot of time and effort negotiating their release. By contrast, when UK had a national kidnapped up there in 2012, we just sent in a (noisy) Shadow and the Shakeys, botched the operation, and burned any humint network we had up there.
However, even if we do find these children, it will not fix the root cause of the problem which is the utterly feckless and corrupt governance in Nigeria. The international community should start on its own doorstep by making it harder for international banks to accept deposits from Nigeria. At the moment, it is only the USA which really vets deposits in its banks from Nigeria. If Nigerians officials were unable to take their stolen money out of the country they would at least be keeping it in the Nigerian economy. Also, there should be bigger fines for companies which pay backhanders to Nigerian officials in order to win contracts - again the USA is leading the way in this by heavily fining any US registered company which pays a bribe in Nigeria. The EU has laws in place but they are not so rigourously enforced. China and Israel are the worst offenders (which is the main reason you see so many Chinese and Israeli arms in Nigeria).
Nigeria is on the way to becoming a failed state and is not far from an all out uprising of poor workers against the staggeringly rich and corrupt officials.