It's easy for new parents to become obsessed with how their baby is developing and growing.
Furthermore, advice on internet forums and from other parents can sometimes be conflicting and confusing.
An important early indicator of potential future health problems for newborns is their birth weight, according to Dr Rakesh Amin, a Consultant Paediatric Endocrinologist at The Portland Hospital and Great Ormond Street Hospital.
"What happens in the womb and
birth weight have major implications for the future," he says.
"For example, if you are born small then you have a much higher chance of problems such as heart disease as an adult."
Babies shouldn't lose more than ten per cent of their birth weight in the first week of life
Around five per cent of children born at term are too small (2.5 kilos and under), or too heavy (four kilos
Dr Amin says that genetics, maternal health, how well the placenta delivers nutrition to the foetus and medical problems in the foetus are all factors which can cause an abnormal birth weight.
Premature babies have added issues, he says, because babies grow a lot in the months and weeks leading up to birth.
"If you are born early, you can’t mimic how well the placenta delivers nutrition - even breast feeding can’t fully make this up," he explains.
All new mothers receive a red book after they've given birth. In this, all of your child's developmental milestones are recorded including weight and height, as well as a list of the vaccinations they receive.
The book contains special charts - which show the normal range of height and weight at each age - so a GP or health visitor can check if your child is growing normally and identify any problems.
"During normal health, babies regularly either change up or down their growth trajectory," explains Dr Amin.
"Most causes of weight loss are minor. The most important thing is repeated weight measurements.
"Babies shouldn’t lose more than ten per cent of their birth weight in the first week of life.
"If they do, that needs urgent medical attention. The cause could be a simple feeding issue such as the quantity and quality of breast milk, but it may also indicate a serious underlying problem."
Apart from weight, the four main developmental areas for babies are: fine motor skills where babies essentially learn to use their fingers and thumbs, for example, to pick up pieces of tissue paper, gross motor skills such as learning to walk, speech and hearing, and sociability - how your child interacts with others.
Newborns are screened at birth for any potential hearing problems.
Parents can also get an accurate assessment of hearing just by noticing how they their child responds to noise on a daily basis.
"A parent’s impression is an important guide," says Dr Amin. "Babies are capable of ignoring you when you speak, but do they turn towards a noise day after day? If they don’t on repeated occasions, then get them tested."
With eyesight, a baby should be fixing their gaze on - and possibly following - your face after six weeks, he adds.
By four months, they should be able to fix on you when you move your head from side-to-side. If they don’t, then something might be wrong.
Dr Mike Thomson, a Consultant in Paediatric Gastroenterology also at The Portland, says delays may occur in one specific area, or across several. And there are many reasons why they develop.
"There are many different possibilities including lack of oxygen around or just before the time of birth, or infections occurring before birth," he explains.
"If you’re worried, talk to a health visitor or GP or request a referral to a paediatrician."
However, don't forget that all babies develop at their own pace.
With eyesight, a baby should be fixing their gaze on - and possibly following - your face after six weeks
For instance, while on average, babies smile at around six weeks, some will smile at four weeks and others at up to ten.
Likewise with sitting: some will do this unaided at six months, while others will not sit until they are between seven and eight months old.
Dr Thomson says: "It's not until we get outside these ranges of developmental progress that paediatricians and children’s carers become concerned."
Another common area of concern for many parents of babies and young children is eating habits.
According to Dr Thomson, the critical time to avoid long-term feeding issues is between about six and 10 months of age when the child's mouth gets experience of different textures.
"Children use eating, especially toddlers, to control their environment and especially their parents," he explains.
"Some children, especially boys, may only eat one certain food at a time, and many children don’t like foods to be mixed together. Fussy eating is a behavioural issue rather than an issue of physical complaint."
His advice is not to confront your child or they will become stubborn. Instead, make sure your child eats at the same time as other family members.
Overfeeding is also an issue, says Dr Amin, and this can trigger meal-time tensions.
"A baby stops eating when it’s full, yet mums and dads continually try to give a child more than they want," he says.
"This becomes overfeeding or a battle. A child will not starve themselves deliberately."
If your baby or toddler isn't gaining weight, then this could indicate a gut disorder which needs medical attention.
Symptoms of gut problems include abdominal pain, diahorrea, constipation and vomiting.
Dr Amin says: "Infants can’t complain so they'll be unsettled. The combination of poor weight gain and an unhappy child needs medical attention."
By Sophie Goodchild