"criminal negligence is an act or failure to act which demonstrates a willful, wanton, or reckless disregard for the safety of others who might reasonably be expected to be injured thereby."
I would say since
A) We know he knows the risks of leaving a child in a hot car as he and his wife admitted to viewing information on the internet on this very thing, Ross stating leaving his son in the car was his biggest fear, he watched a tv show about it.
B)Considering he is in charge of his son's safety, and safe arrival at daycare, and according to him, leaving his son in a hot car was 'his biggest fear', combined with a very short duration of drive time between buckling his son in after breakfast at Chik-fil-a and arriving at work, and the sexting happening at the same time he's to be focusing on getting his son to daycare...
doesn't look like a stretch to prove beyond reasonable doubt a wanton or reckless disregard for the safety of others who might reasonably be expected to be injured thereby
Further, I feel that if his defense is going to go 'sex addiction' angle, that would not soften the impact on me as to his culpability to negligence/second degree child cruelty/felony murder. If Ross were busy enjoying his alcohol addiction, or his meth addiction, while responsible for driving an automobile to breakfast and to work with his child in his care, and his child ended up dead because he 'forgot he was in the car'... none of that would add up to 'it could happen to anyone' to me. Those circumstances happened as they did due to his criminal negligence (if I didn't believe it was premediated.)
Another test I like to do if I wonder should a parent be held criminally responsible in a child's death: If an unrelated to the child, paid babysitter made the same actions the parent did, would they be considered criminally negligent? If Ross's attorneys go the 'so distracted by his sex addiction' route? Exchange Ross for the person who drives the van at the daycare. Keep the sex addiction the same. Jane Doe the daycare van driver was in the throes of her sex addiction/sexting/texting with one of her 6 paramours while she was responsible for Cooper's transportation. A few minutes after buckling Cooper into the van, Jane forgot about him, forgot to get him out of the van, and went into work to continue sexting...exchanging nude images... Her job that morning? To get Cooper safely to the daycare. The one thing she didn't manage to do amidst her 'sex addiction'? Get Cooper safely to daycare. Result. Death of the child in her care.