Edorr
If you are concerned about tubes and your little one you may also want to consider the Transcendent OTL T8-LN 25 watter. The tubes are not open and exposed like many other tube amps. There is a top cover. The amp runs AB bias so it is not nearly as hot as other Class A single ended OTL tube amps, including the Atmasphere and Joule. It idles at 300 watts which is cooler than some Class A SS amps. In addition there is a two week in home trial period.
The amp costs 2.1K and I can't begin to imagine anything at the price that could touch it so far as speed, harmonic integrity at all frequencies and the isolation, spacing and air surrounding instruments and vocals without any traces of grain, hash or noise, dead silent. It is simply amazing. The bass is unbelievable for a 25 watt amp with clearly delineated lines without any overhang. You might ALSO want to talk to Bobby about it. It is absolute magic with the Merlins and I can't recommend it highly enough. I am now using it with Paul Speltz's zero autoformer which effectively raises the impedance of the speaker making it an easier load for the OTL but that is for another thread. Good luck.
Will