You asked

How can I have a safe Halloween with my child ages 2 to 4?

At this age, you should start introducing Halloween to your child as this can also be a start of a new family tradition. But of course, you have to make sure that everything is safe for him or her so that he/she will be able to enjoy the occasion. Here are some things that you should keep in mind when celebrating Halloween with your child aged two to four:
If you are to let your child wear costumes, make sure to choose a costume that is fire-resistant. To avoid getting caught in fire, make sure not to dress your child with something that is too big for him. Also, make sure that flammable materials are out of your child’s reach.
To make sure that your child will not trip, do not make them wear a costume that is to long. Opt for something short to make them feel comfortable as well.
When choosing a costume for your child keep in mind that you might be going to a place that is dark so put something colourful on his clothing; something that can be visible even if it is dark. Also, make sure that you can easily be found by your child so that they will not feel scared.
When choosing props for your child, do not go for something pointed, spiky or hard. Instead, choose something soft or a customised prop you made on your own.
If you plan on using face-paints and your child has not worn them before, test it out first on a small patch of their skin to make sure they do not have a allergic reaction.

More questions

Trick-or-treating can be lots of fun for children but it can sometimes be a scary experience
Halloween can be lots of fun for young children, but many of them might find it a bit too scary.
At this age, you should start introducing Halloween to your child as this can also be a start of a new family tradition.
The best approach on this kind of situation is to be a good example to your baby.
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Your 4-year-old child can already be caught up with all the excitement brought by the holiday season.
Your Christmas traditions can be an extension of your family's personal beliefs and favourite pastimes.
During this stage, your baby is starting to develop her senses and she will definitely be delighted by the sound and lights brought by the season.
Even if your baby is only 30 to 36 months old, he can also be as excited as the rest of the people around him when it comes to celebrating Christmas.