I'm curious about this idea that being uncircumcised invalidates Salah. I am a convert and my son is almost 3, uncircumcised, and was born before I converted. I am divorced from his father and his father is not a Muslim. If it were just up to me, I might choose to have my son circumcised (although personally it really bothers me, I believe it is a Sunnah and that there is great purpose and symbolism in it). I doubt that it's legal to have him circumcised without his father's consent, and despite my religious beliefs about it being highly recommended, I feel like it would be extremely disrespectful and unethical to try and have it done without his father's support. I would go to great lengths to protect my children from any religious body modification that was not from my own religion, and I imagine my son's father would too.
All that said, I can't imagine that his prayers once he reaches the age of accountability will be invalid because of this, although Allahu alim. One can't discount intention and I know that God understands the situation and all factors involved.
I'm inspired to learn more about this now--grateful for that--but as far as I know circumcision is not fard (obligatory) and it is not mentioned in the Qur'an. I'm pretty sure that in some countries it is common to have it done closer to puberty.
With any future sons I have with my current husband, I'm fairly certain we would go to lengths to have him circ'd even if there were laws against it. I would want to wait until at least the 8th day (I think there is great wisdom in that Jewish tradition...it's around that time that the baby's Vit K production kicks in, an important blood-clotter) and I would want someone VERY experienced.