An initial blood test showed nothing but, some weeks ater, Son2's legs started to hurt. At first, we thought it might be a tactic to avoid school but when the pains got worse, I took him back to the GP.
She checked over the last set of blood tests and realised that the paediatrician had missed some important tests. and so ordered a fresh batch.
Now, Son2 and blood tests do NOT go together well. When he got to the nurse, to be told there was no anaesthetic or any kind, he hopped off the bed and decided she wouldn't be taking any blood from him today, thank you very much.
She instead, made him out a prescription for anaesthetic cream, which we had filled, applied and then waited 45 minutes for it to take effect.
Armed with a test-distracting "Where's Wally" the blood was duly taken and within three days, we had the answer.
He had about half the level of Vitamin D in his blood that he should have. Severe deficiency can cause irritability, depression, muscle pains and in the very worst cases, rickets. Luckily, it hadn't got that bad.
He's now on a high dose of Vitamin D supplement for three months.
He's not alone in his deficiency either - parents are encouraged to slap Factor 50 on to their children and keep them out of the sun for fear of melanoma and the increase in fears over child safety and the explosion of computer and console gaming means kids are spending more time indoors. And of course, it's been winter, which doesn't help.
In fact, the BBC recently reported:
The chief medical officer for England, Dame Sally Davies, is to contact medical staff about concerns young children and some adults are not getting enough vitamin D.The problem with Son2 is that he doesn't like the outdoors much. He doesn't like to be near strangers - he doesn't particularly like being with people he knows either.
Government guidelines recommend some groups, including the under-fives, should take a daily supplement. However, recent research found that many parents and health professionals were unaware of the advice.
There has been an increase in childhood rickets over the past 15 years.
According to Dr Benjamin Jacobs, from the Royal National Orthopaedic Hospital, links to heart disease and some cancers are also being investigated. The consultant paediatrician told BBC Breakfast that the hospital saw about one severe case a month of rickets - softening of bones through lack of vitamin D in childhood.
He said: "There are many other children who have less severe problems - muscle weakness, delay in walking, bone pains - and research indicates that in many parts of the country the majority of children have a low level of vitamin D."
The Feeding for Life Foundation report, published in October last year, suggested one in four toddlers in the UK is vitamin D deficient.
He prefers to spend his leisure time in his purple walled, black curtained, disco-balled TechnoLair and attempts to encourage him to go out are usually met with point blank refusal.
The GP, when she looked at Son2's results, said her son was the same so she was going to get him some Vitamin D supplement as well.
I am going to have to try harder not to just let him be in his room, where he's happiest and be tougher on getting him to go out. In fact, I'm just about to send him off to the post box for me on this lovely spring day and I might even go with him as I'm a bit concerned about my own Vitamin D levels.
So, if you're concerned your own kids might be deficient, it wouldn't hurt to get them checked out, or just up their intake of VitD rich food and supplements.
Thank goodness summer's around the corner!