"Springer spaniels are bred to collect prey and bring to the owner uneaten and drop it. It’s much less likely they wouldn’t let go and their inbred instinct is to protect the creature in their mouth whilst bringing it back to the owner."
Only if they are the working gun dog strain(s), I'm afraid. If they're the show dog strain(s), then they may as well be a different breed altogether. The show strain is more inbred than the (original) working one - and, in my experience, far more work to train. Having said that, however, both strains need a lot of experience and work put in to successfully train them. Spaniels - Springers in particular - are renowned for being easily bored, due to their intelligence. Think, 2 year old child on a huge sugar rush...
The Spaniel I spoke about on this thread last week, the one who'd sit on my small son if someone knocked at the door, so that he knew where the lowest member of his pack was in case of danger (and who would have easily gone for the throat of someone trying to hurt either one of my children, too, of that I have never been in any doubt!), was from working stock. His parents and maternal grandmother were all (a) owned and worked in the field by their breeder and (b) champions in their class. By the time he was 5 months old, I'd trained him to understand and follow hand- as well as verbal-signals - and for 13 years, he would watch my hands as well as listen to my voice. If he couldn't hear me (ie, on the school run when strange toddlers would attach themselves to him without permission or warning), he'd watch my hands intently, so focused on that instead of the 2 year old pulling on his ears, or his collar, whilst I remonstrated with their parents. The amount of times I was informed that because my dog was a Spaniel, he would never hurt a child... and the amount of times I pointed out that his breed actually didn't matter - he was a dog, with all the instincts of one, and he was just as capable of snapping at a child's face and scarring them for life as any other dog! Other than the children he lived with, our Spaniel didn't actually have much time for children (he was teased, badly, by neighbouring children when he was a puppy - and never forgot, or forgave them for it!), but he instinctively turned to me - as his trainer, as his leader, as his Mum (for lack of a better definition) - for guidance, reassurance and protection. Had I not been focused on keeping up with his training, then I am fully aware he would, in all likelihood, have bitten one of the toddlers who thought he was a living, breathing toy there, at the school gates, for their amusement alone. I was tempted to bite their ignorant parents, for their inability to watch their own offspring rather than staring at their 'phones for a few minutes, so...!
Also, like Labradors, a Springer has what's known as a "draw bite" - their teeth dig in and draw the flesh towards them, into a hold. Even though these are two of the top 10 dogs to get if you have young children - in my opinion, their bites are the worst. Labradors and Retrievers more so.
Had I not known what I was doing, were I not fully immersed in dog training from the age of 3 years old (when I was given my very first dog - a Lab/Whippet cross), and had I not sourced the breeder of my Spaniel almost 3 years prior to getting him (and gotten to know the proposed parents, and spent time observing them and the maternal grandmother in person), a Springer is probably one of the last breeds I would have gone for with a toddler in the house (they have a low boredom threshold - essentially, even at 12/13 years old, they're like toddlers on a sugar rush!). I did my due diligence, as they say, I didn't wake up one day and think to myself "I want a puppy!" and immediately rush out to buy one. And yes; whilst the Spaniel was a member of the family - just as all of my dogs have been - I am always very conscious of the fact that he was also a dog. Of the damage he could have done to any human had he so chosen to do so. I read books on training him, I sought advice from his breeder - even when our Spaniel was 10 years old, I could call the breeder he came from and ask for advice! - and I worked with him every single day. I put the work in, daily, for 13 years with him, and as a result, he turned out to be a fantastic dog. He could so easily not have been, though. And that would have been on me, for not stepping up and actually putting the effort in with him even when he was past the cute puppy stage.
It's the old adage, I'm afraid, in that a dog is for the duration of their life - not just the cute puppy stage.